Also known as "the Old Man," by his initials "H. M." (a pun on "His Majesty"), or "the Maestro", Merrivale appears in 22 of Carr's locked-room mysteries and "impossible crime" novels of the 1930s, 1940s, and 1950s,[1] as well as in two short stories.
He is a baronet and a barrister – in The Judas Window he actually appears for the defence in court in a murder case – and he holds a medical degree.
Due to the nebulous government position he holds and his eccentric personality, he is thought to have been partially based on Winston Churchill.
He Wouldn't Kill Patience was adapted for the BBC Home Service in 1959, with Felix Felton portraying Sir Henry.
In Anthony Shaffer's play Sleuth, mystery writer Andrew Wyke's most famous character is an aristocratic detective named St. John, Lord Merridew.