Aside from being the most infamous thief the world has ever seen, little is known about Trilby. Even his real name is a mystery to all but himself. The only sure thing the authorities know about Mr. Trilby is that he has a charming personality, always wears a trademark gray suit and matching trilby hat, and was involved in several unexplained murders and disappearances within the supposedly haunted DeFoe Manor, which was recently burned to the ground, and the isolated Welsh Hotel.
Although he is introduced as a master thief, after the events of 5 Days a Stranger, which happened to him only by chance after he broke into DeFoe Manor, he gave up the thieving life, apparently unable to break into any home, no matter how harmless, without the paranoid feeling that something terrible and supernatural might happen to him again. At some point after this, he became an agent of a nameless agency that deals with the supernatural, Trilby's unique skillset coming in handy for a secretive organization.
He focused on the case of the Welder, the murderous ghost of the retarded son of Roderick DeFoe, a boy who had never been given a name by his father, who was so ashamed of having a disabled child that he chained him to the wall of a cellar and kept him sealed there for years. The murderous rage the boy, whom Trilby would posthumously dub "John DeFoe", felt towards the entire world, not understanding why he had to suffer so, manifested in the form of his ghost possessing people, who would then don the only objects John had ever thought of as his, a welder's mask and apron, and then use a knife to murder the first person they come across.
Eventually realizing that John's hatred for everything and everyone would never subside, Trilby saw to it that the artifact that contained his spirit, a small wooden idol, was launched into space and pushed off in a random direction, the frictionless nature of space meaning it could theoretically travel for hundreds of thousands of years before ever stopping. In this way, Trilby hoped to free the world of John DeFoe's horrific spectre, but in reality, it was part of the twisted machinations of the Cthulhu-like entity known as Chzo, who had arranged everything thousands of years in advance, in order to transform Theo DaCabe, an ordinary man, into its New Prince, a mysterious avatar of sorts.
After the conclusion of the Chzo Mythos, Trilby: The Art of Theft, a prequel to the entire series, was released. Entirely unrelated to Chzo or John DeFoe, The Art of Theft is a stealth-action game depicting Trilby's former life as a master thief, and has a fairly standard "break in, avoid guards, steal items, get out undetected" theme.