| His Royal Highness|
| King of Thailand|
| Amphorn Sathan Residential Hall, Dusit Palace, Bangkok|
Life tenure or until accession as Sovereign
The Crown Prince of Thailand (or Siam; Thai: สยามมกุฎราชกุมาร; rtgs: Sayammakutratchakuman) is a title held by the heir apparent to the Thai throne. First created by King Chulalongkorn (Rama V) in 1886, for his son Prince Maha Vajirunhis, the king's eldest son by a royal wife Queen Savang Vadhana. Prior to this, the Siamese throne did not have a law or formal system regulating the royal succession. In 1688 King Petracha of Ayutthaya created the title of Front Palace, which by the Rattanakosin period had become the main title granted to the heir presumptive to the throne. However few Front Palaces have succeeded to the throne this way, with the exception of King Buddha Loetla Nabhalai (Rama II) in 1809. After the Front Palace crisis in 1875, the title of Front Palace was abolished and replaced with the title of Crown Prince, who became heir apparent to the throne.
In 1924 King Vajiravudh (Rama VI) promulgated the 1924 Palace Law of Succession to regulate the succession, this law essentially barred females, children of commoner wives or children of foreign wives to the throne, it also re-affirmed Agnatic Primogeniture, or succession through the male-line by seniority. This law also affected the individuals who could become Crown Prince. Since its creation three Princes have been raised to this title, and two have succeeded to the throne.
Crown Prince of Thailand Wikipedia
List of heirs apparent and heirs presumptive since 1886, those in bold succeeded to the throne as King.