The 64-year-old, who is the king's only son, will succeed a much-loved monarch, assuming a role many in Thailand regard as semi-divine.
But there are fears the new king will not have the same authority as his father.
The crown prince's colourful lifestyle and the country's current political instability mean a smooth succession is not guaranteed.
Thailand has strict lese majeste laws which protect the royal family from insult or threat. They have largely shielded the monarchy, including the crown prince, from public view or scrutiny.
Most ordinary Thais know only a few details about who he is and how he lives his life.