[4] In a letter to Frank Morley, Eliot wrote, "I have done a new cat modeled on the late Professor Moriarty, but he doesn't seem very popular; too sophisticated perhaps.

Beginning: Macavity's a Mystery Cat: he's called the Hidden Paw - For he's the master criminal who can defy the Law.

[3][4] According to the poem, even when the Secret Service decides that Macavity was behind a loss, they are unable to apprehend him, as "he's a mile away", "...[or] engaged in doing complicated long division sums".

The poem also says: "His brow is deeply lined in thought, his head is highly domed; His coat is dusty from neglect, his whiskers are uncombed."

He is extremely tall and thin, his forehead domes out in a white curve, and his two eyes are deeply sunken in his head...his face protrudes forward and is forever oscillating from side to side in a curiously reptilian fashion.The poem accuses Macavity of misbehaviour that would be within the capabilities of an ordinary cat, such as stealing milk, but also holds him responsible for major crimes.

He is referred to as a "fiend in feline shape, a monster of depravity" and has been suspected of stifling Pekes, vandalism, theft, cheating at cards, espionage and controlling an organised crime ring with Mungojerrie, Rumpleteazer and Griddlebone among the members.

Webster and Starr assumed that Eliot referred to the cases of Mr. Joseph Harrison (The Adventure of the Naval Treaty) and Herr Hugo Oberstein (The Adventure of the Bruce-Partington Plans) when he wrote in the poem – "And when the Foreign Office finds a Treaty's gone astray,/ And the admirality loses some plans and drawings by the way".

[17] Macavity is typically depicted as a cat with a chaotic array of red, orange, white, and sharp black stripes.

The role of Macavity is usually played by the same actor as Plato (a chorus cat who notably does a pas de deux with Victoria during the Jellicle Ball).

Admetus/Plato is also often recognisable as one of the tallest cast members, as the fight scene between Macavity and Munkustrap requires him to be able to lift other male dancers.

Gillian Robert's schoolteacher detective Amanda Pepper has an elderly male companion cat whose métier seems to be relaxation.

[18] The following books by Roberts feature Macavity the cat: Claire and Present Danger (2003), Helen Hath No Fury (2001), Adam and Evil (1999), The Bluest Blood (1998), The Mummer's Curse (1996), How I Spent My Summer Vacation (1995), In the Dead of Summer (1995), With Friends Like These… (1993), I'd Rather Be in Philadelphia (1992), Philly Stakes (1989), Caught Dead in Philadelphia (1987).