John Creasey MBE (17 September 1908 – 9 June 1973) was an English crime and science fiction writer who wrote more than six hundred novels using twenty-eight different pseudonyms.

He created several characters which are now famous, such as The Toff (The Honourable Richard Rollison), Commander George Gideon of Scotland Yard, Inspector Roger West, The Baron (John Mannering), Doctor Emmanuel Cellini and Doctor Stanislaus Alexander Palfrey. The most popular of these was Gideon of Scotland Yard, who was the basis for the television series Gideon's Way and for the John Ford movie Gideon of Scotland Yard (1958), also known by its British title Gideon's Day.

His pseudonyms include:

Westerns under the names of Ken Ranger, Tex Riley, William K. Reilly, and Jimmy Wilde. Romantic novels under the names of Margaret Cooke, M.E. Cooke, and Elise Fecamps.

I read his books years ago, The Toff, The Baron, Inspector Gideon. Loved all of them. 

I don't though ever remember reading the Inspector West or Doctor Palfrey books. Might see if they are available to read on Hoopla.

I thought that Georges Simenon was the most prolific author but it looks like Creasey may be the champ in that regard.