From UO Second Age
A monster called a slime exists in-game which is a small slithering blob. Early in UO's history, it was possible to encounter a slime that was renamed to "jwilson," which was purportedly named after magazine editor Johnny Wilson, who had given Ultima Online a bad review and thus earned a derisive place in the game by the developers. They were removed and unavailable in the live game for years, but made a return in late 2007.
JWilson's existed throughout the T2A era.