Bugs Bunny, the court jester of King Arthur, must recover a singing sword from Yosemite Sam (as the Black Knight) and his fire-breathing, often sneezing, dragon. The film is a partial remake of Freleng's earlier Sahara Hare, which was also largely about Bugs inside a building (in that case, a fort) and Sam on the outside, repeatedly trying (and failing) to get inside.
King Arthur is sitting with his Knights of the Round Table, complaining about hard times that have befallen the kingdom ever since the Black Knight stole the Singing Sword. He asks his knights—among them Sir Osis of Liver and Sir Loin of Beef—for a volunteer to get the sword back. The knights complain that the Black Knight is invincible and has a fire-breathing dragon guarding the sword. King Arthur angrily demands to know if the knights are all chicken, and is dismayed when he hears clucking and sees chicken feathers flying. Bugs, dressed as a court jester, dances in and tells King Arthur that "only a fool" would be crazy enough to go after the Singing Sword. The King agrees ("A good idea, fool."), and tells Bugs that he has to get the singing sword, or else face being executed ("Put to the rack, burned at the stake, and beheaded"). Bugs at first laughs at the idea, but then starts crying when he realizes that the king is serious.
At the castle of the Black Knight—shown to be Yosemite Sam dressed in black armor—there is a fire-breathing dragon that belongs to Sam, but the dragon has come down with a cold from allowing its fire to get low, and thus, is prone to fits of sneezing, causing jets of flame to shoot from its nostrils. Sam feeds the dragon some coal to fuel the dragon's internal fire, and then goes back to taking a nap on his chair. Bugs sneaks in to the castle, past Sam and the dragon and to the chest where he pulls out the singing sword. He openly wonders why it's called a "singing sword" and finds out when it starts vibrating, via a musical saw, to the tune of "Cuddle up a Little Closer, Lovey Mine". Sam wakes up and chases Bugs, but Bugs slams the door in Sam's face, causing his armor to fall off. Sam then wakes up the dragon ("Wake up, you fire-breathing lizard!"), who unintentionally breathes fire on him ("And stop breathing on me, you idjit!").
Bugs runs outside the castle, chased by Sam on the dragon. Bugs ducks into a hole, and Sam slides off the dragon when trying to stop. Bugs then runs back to the castle and raises the drawbridge as Sam approaches, causing Sam to fall into the moat. When Sam demands that Bugs lowers the drawbridge, Bugs lowers it right onto Sam's head, who yells in a muffled voice to raise it back up again. A flat Sam shouts: "Okay, rabbit! You've forced me to use force!" Sam then uses the dragon to pull a catapult in place, gets on it and launches himself to the castle, but misses the window Bugs is looking out of, flattening his front (In a "cramped" voice, Sam declares: "You'll pay for this, varmint!"). Next, Sam lassos a rope around one of the battlements of the castle, but as he is climbing up, Bugs whacks Sam on the head with a mallet ("Now, let's see if I remember. Head down, left arm stiff."), causing Sam to slide down the rope outside of his armor.
Thinking the coast is clear, Bugs sneaks out of the castle. Sam and his dragon are hidden behind a rock waiting for Bugs, but the dragon sneezes on Sam again, alerting Bugs to their presence. Bugs then runs back into the castle, followed by Sam and the dragon. Bugs runs into a room, Sam and the dragon follow, then Bugs sneaks out and locks the door to what is now shown as an explosives room. Surrounded by all kinds of explosives, Sam tries to keep the dragon from sneezing again ("Aagh! Don't sneeze, you stupid dragon, or you'll blow us to the moon!"). As Bugs walks away from the castle, the dragon sneezes again, and the tower Sam and the dragon are in takes off like a rocket, flying towards the moon (Sam glares at the befuddled dragon and says, "Dragons is so stupid!"). Bugs waves goodbye, saying: "Farewell to thee". The singing sword picks up on this and starts humming "Farewell to Thee" as Bugs walks out of sight, ending the cartoon.
Among all of the Bugs Bunny cartoons, this is the only one to win the Academy Award for Best Animated Short in 1959. In doing so, it beat out cartoons Walt Disney Studios' Paul Bunyan and Terrytoons' Sidney's Family Tree. It was the third Oscar-nominated Bugs Bunny cartoon, after A Wild Hare in 1940 and Hiawatha's Rabbit Hunt in 1941. The Oscar was presented to John W. Burton, the producer of this cartoon.
In the Tiny Toon Adventures episode "Who Bopped Bugs Bunny?", the Oscar win of Knighty Knight Bugs is a major plot point. It is revealed that in 1959, a cartoon of Sappy "Slaphappy" Stanley (an elephant, voiced by Jonathan Winters) was defeated for the "Sclockser" (a parody of the Oscar) award by Knighty Knight Bugs. As a result, Stanley scorned the US film industry and relocated to France, where he became a national star (parodying the similar career move of Jerry Lewis), but he still nursed a bitter grudge against Bugs, culminating in the episode's plot. Sappy Stanley is not a pre-existing cartoon character, having been created for the episode, but a parody of Terrytoons character Sidney the Elephant, a.k.a. "Silly Sidney", whose cartoon Sidney's Family Tree was indeed nominated for an Academy Award the same year as Knighty Knight Bugs.The phrase "Sir Loin of Beef" was used in Bugs Bunny parody Rabbit Hood by Bugs to con the gullible Sherriff of Nottingham.
The phrase "Sir Osis of the Liver" was used in the Bugs Bunny parody Knight-mare Hare.
The gag on a dopey fire breathing dragon was also used in Knight-mare Hare and on the cartoon series Here Comes the Grump.
This cartoon is featured uncut on Disc 1 of the Looney Tunes Golden Collection: Volume 4 DVD set, Warner Bros. Home Entertainment Academy Awards Animation Collection, and The Essential Bugs Bunny. It is also available in the Looney Tunes Platinum Collection: Volume 3 Blu-ray and DVD.
Bugs' White Water Rapids is a Hopkins Rides log flume themed to Knighty Knight Bugs that opened in 1998 at Six Flags Fiesta Texas in San Antonio, Texas.