Sitthikorn "Sia Ood" Boonchim, a wealthy trader convicted and jailed for unlicensed use of royal insignia to produce and sell amulets, has been found dead in a hotel in Phitsanulok province.
Police said it appeared he committed suicide.
Sitthikorn, 44, was found lying face down in a room at a hotel in Muang district of the northern province on Friday. A handwritten farewell letter was found inside the room, police said.
It was estimated he had died two days before his body was discovered. There were no traces of a struggle in the room.
In the letter, he said he was proud he had made a fortune despite being an orphan. He said he had made enormous contributions to religion and society, according to police. In the letter, Sitthikorn claimed he had donated over 3 billion baht to charity activities across the country.
He also said he felt sad that he had previously helped other people, but got a bad reputation and insincerity in return, according to police.
He asked his younger brother to have his body cremated immediately, without any religious rites.
Police investigators said Sitthikorn had checked in to the hotel on Oct 21.
Police found 20 packs of Alprazolam, a medication used to treat anxiety and panic disorders, and other medicine for treating cancer, inside the room. Of the 20 packs of Alprazolam, 10 were empty.
The hotel owner, who declined to be named, said Sitthikorn, was accompanied by a young man identified later as Suraphan Modthai when he first checked in.
Three days ago, Sitthikorn had told a hotel maid that he did not want to be disturbed, the hotel owner said.
Mr Suraphan, 23, told police that he had known the amulet trader since 2013 and they had regularly been in touch. He visited Sitthikorn several times at the hotel, taking him out for meals and bring him clean clothes.
He had last seen the amulet trader on Tuesday afternoon, when they had a mealtogether, he said.
When Sitthikorn had failed to contact him as usual, he went to his room late on Thursday night and knocked on the room door several times, but there was no answer.
He then contacted hotel staff, who later found Sitthikorn dead in the room.
Sitthikorn, better known as Sia Ood, was released from jail on June 20, 2013 after serving a five-year sentence for a fraud conviction.
The amulet trader was jailed in 2008 for cheating the public by using the royal insignia without permission to produce and sell Somdej Nau Hua amulets.
Sia Ood was known to the public as a benefactor of young male entertainers, including popular actors and singers.