Wodehouse said in a 1955 letter that Aunt Agatha was inspired by his maternal aunt Mary Bathurst Deane, "who was the scourge of my childhood".
As a boy Wodehouse lived with his grandmother and four unmarried aunts (including Aunt Mary). This inspired the setting of The Mating Season, where Bertie finds himself staying in a house infested by five aunts.
The Other Darrin: Over four seasons, two different actors play Gussie, three different actors play Madeline, two play Agatha, two Barmy, four Dahlia, two Claude, two Eustace, and two Bingo - just to name a few. Even Bartholomew changes: in his first appearances, he's a Scottish terrier (black). When he comes back, he's a Westie (white).
Reaches Mind Screw levels when you realize that the first Madeline comes back as the second Florence. Especially bizarre in the last episode where the two characters actually share scenes.
Uncredited Role: Rosalind Knight as a hotel proprietress in "Will Anatole Return to Brinkley Court? (or, the Matchmaker)".
Francesca Folan originally played Madeline Bassett in Season 1, but then returned to play Florence Craye in Season 4.
Richard Braine played Steggles in Season 1, then played Gussie in Seasons 3 and 4.
Other trivia
In Bertie In Love, Jeeves identifies Aunt Agatha's dog Macintosh as an Aberdeen Terrier. The animal on screen is actually a West Highland Terrier, a related but distinct breed.
, "who was the scourge of my childhood".