William Monk.

Born in Northumberland, his father worked on the sea.  He has one sister, Beth, married with children, but he scarcely knows her.

Monk lost his memory completely in a coach accident in 1856 in Face of a Stranger - hence the title.  He never regained it, but does learn a lot about himself, much of it less than flattering.  He is extremely clever, but in the past has been ruthless in his climb to the top of his profession as a police detective.  His abrasive personality actually prevented his promotion, although he did not realize it.

He met Hester Latterly, a young woman with a character every bit as abrasive as his own, a courage just as powerful.  She had worked with Florence Nightingale in the Crimean War, and is Monk's match.  It takes him some time to realize this, as it does her also.  Eventually they do marry.  He asks her at the end of 'A Breach of Promise', and by this time they are both wiser and mellower - but not without a few edges left.

Monk detects a good deal of his past, during one adventure or another and his flashes of memory.  He was originally in banking, with a driving desire to become a gentleman, then an event in his life turned him towards the police, at which he turned out to excel.

After several quarrels with his superior, Runcorn, he was dismissed (or quit - depending on whose version you take - his or Runcorn's).  He then took up private enquiry, but it was an erratic living, and finally the opportunity offered itself to join the Thames River Police, with a whole new collection of challenges, a new scene for detection, and command of men - not his greatest skill!  Much to challenge him, much to learn.