The best-known story of the twins' birth is that Zeus disguised himself as a swan and seduced Leda. Thus Leda's children are frequently said to have hatched from two eggs that she then produced. The Dioscuri can be recognized in vase-paintings by the skull-cap they wear, the pilos, which was explained in antiquity as the remnants of the egg. Whether the children are thus mortal or half-immortal is not consistent among accounts, nor is whether the twins hatched together from one egg. In some accounts, only Pollux was fathered by Zeus, while Leda and her husband Tyndareus conceived Castor. This explains why they were granted an alternate immortality. It is a common belief that one would live among the gods, while the other was among the dead. The figure of Tyndareus may have entered their tradition to explain their archaic name Tindaridai in Spartan inscriptions or in literature Tyndaridai, in turn occasioning incompatible accounts of their parentage.
Castor and Pollux are sometimes both mortal, sometimes both divine. One consistent point is that if only one of them is immortal, it is Pollux. In Homer's Iliad, Helen looks down from the walls of Troy and wonders why she does not see her brothers among the Achaeans. The narrator remarks that they are both already dead and buried back in their homeland of Lacedaemon, thus suggesting that at least in some early traditions, both were mortal. Their death and shared immortality offered by Zeus was material of the lost Cypria in the Epic cycle.
The Dioscuri were regarded as helpers of humankind and held to be patrons of travellers and of sailors in particular, who invoked them to seek favourable winds. Their role as horsemen and boxers also led to them being regarded as the patrons of athletes and athletic contests. They characteristically intervened at the moment of crisis, aiding those who honoured or trusted them.
Both Dioscuri were excellent horsemen and hunters who participated in the hunting of the Calydonian Boar and later joined the crew of Jason's ship, the Argo.
During the expedition of the Argonauts, Pollux took part in a boxing contest and defeated King Amycus of the Bebryces, a savage mythical people in Bithynia. After returning from the voyage, the Dioskouroi helped Jason and Peleus to destroy the city of Iolcus in revenge for the treachery of its king Pelias.
When their sister and half-sister Helen was abducted by Theseus, the half-brothers invaded his kingdom of Attica to rescue her. In revenge they abducted Theseus's mother Aethra and took her to Sparta while setting his rival, Menestheus, on the throne of Athens. Aethra was then forced to become Helen's slave. She was ultimately returned to her home by her grandsons Demophon and Acamas after the fall of Troy.
Castor and Pollux aspired to marry the Leucippides ("daughters of the white horse"), Phoebe and Hilaeira, whose father was a brother of Leucippus ("white horse"). Both women were already betrothed to cousins of the Dioscuri, the twin brothers Lynceus and Idas of Thebes, sons of Tyndareus's brother Aphareus. Castor and Pollux carried the women off to Sparta wherein each had a son; Phoebe bore Mnesileos to Pollux and Hilaeira bore Anogon to Castor. This began a family feud among the four sons of the brothers Tyndareus and Aphareus.
The cousins carried out a cattle-raid in Arcadia together but fell out over the division of the meat. After stealing the herd, but before dividing it, the cousins butchered, quartered, and roasted a calf. As they prepared to eat, the gigantic Idas suggested that the herd be divided into two parts instead of four, based on which pair of cousins finished their meal first. Castor and Pollux agreed. Idas quickly ate both his portion and Lynceus' portion. Castor and Pollux had been duped. They allowed their cousins to take the entire herd, but vowed to someday take revenge.
Some time later, Idas and Lynceus visited their uncle's home in Sparta. The uncle was on his way to Crete, so he left Helen in charge of entertaining the guests, which included both sets of cousins, as well as Paris, prince of Troy. Castor and Pollux recognized the opportunity to exact revenge, made an excuse that justified leaving the feast, and set out to steal their cousins' herd. Idas and Lynceus eventually set out for home, leaving Helen alone with Paris, who then kidnapped her. Thus, the four cousins helped set into motion the events that gave rise to the Trojan War.
Meanwhile, Castor and Pollux had reached their destination. Castor climbed a tree to keep a watch as Pollux began to free the cattle. Far away, Idas and Lynceus approached. Lynceus, named for the lynx because he could see in the dark, spied Castor hiding in the tree. Idas and Lynceus immediately understood what was happening. Idas, furious, ambushed Castor, fatally wounding him with a blow from his spear—but not before Castor called out to warn Pollux. In the ensuing brawl, Pollux killed Lynceus. As Idas was about to kill Pollux, Zeus, who had been watching from Mt. Olympus, hurled a thunderbolt, killing Idas and saving his son.
Returning to the dying Castor, Pollux was given the choice by Zeus of spending all his time on Mount Olympus or giving half his immortality to his mortal brother. He opted for the latter, enabling the twins to alternate between Olympus and Hades. The brothers became the two brightest stars in the constellation Gemini ("the twins"): Castor (Alpha Geminorum) and Pollux (Beta Geminorum). As emblems of immortality and death, the Dioskouri, like Heracles, were said to have been initiated into the Eleusinian mysteries.
Castor and Pollux are consistently associated with horses in art and literature. They are widely depicted as helmeted horsemen carrying spears. The Pseudo-Oppian manuscript depicts the brothers hunting, both on horseback and on foot.
On votive reliefs they are depicted with a variety of symbols representing the concept of twinhood, such as the dokana (δόκανα – two upright pieces of wood connected by two cross-beams), a pair of amphorae, a pair of shields, or a pair of snakes. They are also often shown wearing felt caps, sometimes with stars above. They are depicted on metopes from Delphi showing them on the voyage of the Argo (Ἀργώ) and rustling cattle with Idas. Greek vases regularly show them capturing Phoebe and Hilaeira, as Argonauts, as well as in religious ceremonies and at the delivery to Leda of the egg containing Helen. They can be recognized in some vase-paintings by the skull-cap they wear, the pilos (πῖλος), which was already explained in antiquity as the remnants of the egg from which they hatched.
The Dioskouri were worshipped by the Greeks and Romans alike; there were temples to the twins in Athens, such as the Anakeion, and Rome, as well as shrines in many other locations in the ancient world.
The Dioskouri and their sisters grew up in Sparta, in the royal household of Tyndareus; they were particularly important to the Spartans, who associated them with the Spartan tradition of dual kingship and appreciated that two princes of their ruling house were elevated to immortality. Their connection there was very ancient: a uniquely Spartan aniconic representation of the Tyndaridai was as two upright posts joined by a cross-bar; as the protectors of the Spartan army the "beam figure" or dókana was carried in front of the army on campaign. Sparta's unique dual kingship reflects the divine influence of the Dioscuri. When the Spartan army marched to war, one king remained behind at home, accompanied by one of the Twins. "In this way the real political order is secured in the realm of the Gods".
Their herōon or grave-shrine was on a mountain top at Therapne across the Eurotas from Sparta, at a shrine known as the Meneláeion where Helen, Menelaus, Castor and Pollux were all said to be buried. Castor himself was also venerated in the region of Kastoria in northern Greece.
They were commemorated both as gods on Olympus worthy of holocaust, and as deceased mortals in Hades, whose spirits had to be propitiated by libations. Lesser shrines to Castor, Pollux and Helen were also established at a number of other locations around Sparta. The pear tree was regarded by the Spartans as sacred to Castor and Pollux, and images of the twins were hung in its branches. The standard Spartan oath was to swear "by the two gods" (in Doric Greek: νά τώ θεὼ, ná tō theō, in the Dual number).
The rite of theoxenia (θεοξενία), "god-entertaining", was particularly associated with Castor and Pollux. The two deities were summoned to a table laid with food, whether at individuals' own homes or in the public hearths or equivalent places controlled by states. They are sometimes shown arriving at a gallop over a food-laden table. Although such "table offerings" were a fairly common feature of Greek cult rituals, they were normally made in the shrines of the gods or heroes concerned. The domestic setting of the theoxenia was a characteristic distinction accorded to the Dioskouri.
The image of the twins attending a goddess are widespread and link the Dioskouri with the male societies of initiates under the aegis of the Anatolian Great Goddess. and the great gods of Samothrace. The Dioscuri are the inventors of war dances, which characterize the Kuretes.
The heavenly twins appear also in the Indo-European tradition as the effulgent Vedic brother-horsemen the Ashvins, the Lithuanian Ašvieniai, and the Germanic Alcis.
From the fifth century BC onwards, the brothers were revered by the Romans, probably as the result of cultural transmission via the Greek colonies of Magna Graecia in southern Italy. An archaic Latin inscription of the sixth or fifth century BC found at Lavinium, which reads Castorei Podlouqueique qurois ("To Castor and Pollux, the Dioskouri"), suggests a direct transmission from the Greeks; the word "qurois" is virtually a transliteration of the Greek word κούροις, while "Podlouquei" is effectively a transliteration of the Greek Πολυδεύκης. The construction of the Temple of Castor and Pollux, located in the Roman Forum at the heart of their city, was undertaken to fulfil a vow (votum) made by Aulus Postumius Albus Regillensis in gratitude at the Roman victory in the Battle of Lake Regillus in 495 BC. The establishing of the temple may also be a form of evocatio, the transferral of a tutelary deity from a defeated town to Rome, where cult would be offered in exchange for favor. According to legend, the twins fought at the head of the Roman army and subsequently brought news of the victory back to Rome. The Locrians of Magna Graecia had attributed their success at a legendary battle on the banks of the Sagras to the intervention of the Twins. The Roman legend may in fact have had its origins in the Locrian account and possibly supplies further evidence of cultural transmission between Rome and Magna Graecia.
The Romans believed that the twins aided them on the battlefield. Their role as horsemen made them particularly attractive to the Roman equites and cavalry. Each year on July 15, the feast day of the Dioskouri, the 1,800 equestrians would parade through the streets of Rome in an elaborate spectacle in which each rider wore full military attire and whatever decorations he had earned.
In translations of comedies by Plautus, women generally swear by Castor, and men by Pollux; this is exemplified by the slave-woman character Staphyla in A Pot of Gold (act i, ll.67-71) where she swears by Castor in line 67, then the negative prefix in line 71 denotes a refutation against swearing by Pollux.
The Etruscans venerated the twins as Kastur and Pultuce, collectively the tinas cliniiaras, "sons of Tinia," the Etruscan counterpart of Zeus. They were often portrayed on Etruscan mirrors. As was the fashion in Greece, they could also be portrayed symbolically; one example can be seen in the Tomba del Letto Funebre at Tarquinia where a lectisternium for them is painted. They are symbolised in the painting by the presence of two pointed caps crowned with laurel, referring to the Phrygian caps they were often depicted wearing.
Even after the rise of Christianity, the Dioskouroi continued to be venerated. The fifth-century pope Gelasius I attested to the presence of a "cult of Castores" that the people did not want to abandon. In some instances, the twins appear to have simply been absorbed into a Christian framework; thus fourth-century AD pottery and carvings from North Africa depict the Dioskouroi alongside the Twelve Apostles, the Raising of Lazarus or with Saint Peter. The church took an ambivalent attitude, rejecting the immortality of the Dioskouroi but seeking to replace them with equivalent Christian pairs. Saints Peter and Paul were thus adopted in place of the Dioskouroi as patrons of travelers, and Saints Cosmas and Damian took over their function as healers. Some have also associated Saints Speusippus, Eleusippus, and Melapsippus with the Dioskouroi.
The New Testament scholar Dennis MacDonald identifies Castor and Pollux as basis characters for the appearance of James son of Zebedee and his brother John who appear in the narrative by Mark the Evangelist. MacDonald cites the origin of this identification to 1913 when J. Rendel Harris published his work Boanerges, a Greek term for Thunder, the epithet of Zeus father of Pollux in what MacDonald calls a form of early Christian Dioscurism.
More directly, the Acts of the Apostles mentions the Dioskouroi in a neutral context, as the figurehead of an Alexandrian ship boarded by Paul in Malta (Acts 28:11).
Castor and Pollux were the names of two elephants, believed to have been brothers, who resided in a Parisian zoo during the mid 19th century. The unfortunate pair were eventually sold, butchered, and eaten in a famous incident during food shortages caused by the Prussian Siege of Paris in 1870.
Two brothers named Castor and Pollux Troy feature in the movie Face/Off. Castor is the main antagonist in the movie and Pollux is somewhat of a sidekick to him, so the reference may be ironic.
In The Hunger Games, Castor and Pollux are brothers who make up Cressida's camera crew from the Capitol.
There is also a pair of twins named Castor and Pollux in the Percy Jackson books. They are children of Dionysus, Greek god of wine, grapes, fertility, madness and theatre. Castor is killed during the Battle of the Labyrinth in The Battle of the Labyrinth.
In Homestuck, the Gemini troll is named Sollux Captor, switching the S and P around.
In Orphan Black, a program for male clones is named Castor, and all of the clones are branded with a two-headed horse. A program for female clones is called Leda.
In the School for Good and Evil, Pollux and Castor are a massive dog with two heads, one as Pollux and the other Castor. One teaches at the School for Good, the other Evil.
In the videogame Tales From the Borderlands, the heroes of the story encounter a general named Pollux in stasis, however there is no mention of Castor.