The film's title character is not invented. Apichatpong Weerasethakul based Uncle Boonmee on a real book, A Man Who Can Recall His Past Lives, written in 1983 by the Buddhist abbot Phra Sripariyattiweti. The abbot's book recounts the case of a layman, Boonmee, who approached him claiming that while meditating he could clearly remember a sequence of his own former lives, an experience the abbot recorded and published as an account worth examining rather than dismissing outright. Weerasethakul read it years before he began the film and eventually traveled to the area to search for the real Boonmee's surviving relatives and to learn what he could about the actual man behind the book's claim.
What the film keeps from that source is the structure, not a strict biography. Its own Boonmee is dying of kidney failure at a farm in Thailand's northeastern Isan region, and as his family gathers he begins to see, and to be seen by, figures the film treats with the same unhurried realism as everything else on screen: the ghost of his dead wife returning to sit at the dinner table, and his long missing son, transformed years earlier into a red eyed, ape like spirit of the jungle. Boonmee attributes his illness to karma, specifically to communists he killed and insects he destroyed farming across his own lifetime, a plainly Buddhist accounting of cause and consequence carried by a dying man doing the arithmetic on his own life rather than by any character preaching it to him. The abbot's premise, that a person's past lives remain genuinely accessible to memory, becomes in Weerasethakul's hands a family drama conducted as though that premise were simply true.