Guilty
Guilty is the cat belonging to Mrs Tachyon, the mysterious trolley-lady in Johnny and the Bomb. In appearance, he/she/it (nobody has dared look to check or considered the risk is worth it) is a white cat, with brown patches, and three-and-a-half legs. Guilty is first encountered in May 1941, as living proof of the reality of the Schrödinger's Cat theory, as a yellow-eyed demonic entity screaming out of the depths of the trolley to wreak vengeance on a hapless Army bomb disposal private. Deciding that he isn't paid nearly enough to defuse bombs of this terrifying sort, the EO soldier beats a very wise retreat, and ignores the fact that the real bomb has just started to tick. Either Guilty or Mrs Tachyon is aware enough to notice, however, and they beat a very hasty retreat of their own to the late 1990's. It isn't quick enough for Mrs Tachyon, who is injured by the blast and ends up in the local hospital. Johnny Maxwell takes care of the Trolley, and, by extension, of Guilty, who is a cat of firm views about catfood - ie, this happens to other cats. It is possible that Guilty is the extension, into Roundworld's reality of space and time, of the universal phenomenon which is Greebo. He/she/it is very definitely a Real Cat, accustomed to living on a diet of greasy fish and chips out of newspaper wrapping with, if anyone took the trouble to look, very odd dates on it...
Just as Foul Ole Ron has a thinking-brain dog (Gaspode), is it possible that Guilty, who at the very least acts as bodyguard to his/her/its source of greasy chips, is the thinking-brain cat to Mrs Tachyon?