Social critic Sulak Sivaraksa may face a lese majeste charge for comments he made about King Naresuan's 16th-century elephant duel.
Two retired soldiers, Lt Col Padung Niwetwan and Lt Col Pittaya Wimalin, filed the complaint against Mr Sulak at Chana Songkhram Police Station on Thursday. They said he dishonoured King Naresuan at a seminar at Thammasat University on Oct 5.
Pol Lt Col Somyot Udomraksasap, investigation inspector from Chana Songkhram Police Station, confirmed the complaint was filed.
The two retired officials who filed the complaint told police that Mr Sulak may have violated the lese majeste law for encouraging people to question if the duel, recorded in the history of the monarch, actually happened, considering nobody witnessed it.
They told police Mr Sulak said other things during the seminar that could be considered offensive, but didn't go into details.
Mr Sulak, 82, has twice been charged with lese majeste after speaking at a seminar at Silpakorn University in 2004 and at another at Khon Kaen University in 2007. He has never been convicted.
Army spokesman Winthai Suwaree said the two retired officers did not represent the army or the National Council for Peace and Order, saying they filed the complaint in a personal capacity.
Under the law, anyone can file a lese majeste complaint against someone.
Human rights lawyer Somchai Homlaor said a person would be charged with lese majeste only if he or she defames, insults or threatens the king, queen, heir apparent or the regent, he said.
The law is unlikely to apply to a historical monarch such as King Naresuan.
Mr Somchai said police are required to record the complaints, but Mr Sulak probably will not see jail time.
A ruling is expected on Thursday.