Wikipedia

Rising Damp starred Leonard Rossiter, Frances de la Tour, Richard Beckinsale and Don Warrington.[4] Rossiter played Rupert Rigsby (originally Rooksby in the stage play), the miserly, seedy, and ludicrously self-regarding landlord of a run-down Victorian townhouse who rents out his shabby bedsits to a variety of tenants. Beckinsale played Alan Moore, a long-haired, naive, good-natured and amiable medical student who occupies the top room. Frances de la Tour played Ruth Jones, a fey, whimsical spinster and college administrator who rents another room, is approaching middle age, and with whom Rigsby is in love.

In the pilot episode, a new tenant arrives. Philip Smith (Don Warrington) is a planning student who claims to be the son of an African Chief. As a black man, he brings out the ill-informed fears and knee-jerk suspicions of Rigsby. However, the landlord quickly accepts his new tenant and henceforth regards him with a wary respect... wary because of Philip's intelligence and smooth manners, and especially because Miss Jones finds herself attracted to the handsome sophisticate. Of these four principal actors, only Beckinsale was a new recruit – the others had all played their roles in the original stage play.

In the first series, there was another tenant Spooner, a professional wrestler, played by Derek Newark. Rigsby gets on his bad side when he and Alan 'borrow' his clothes in the episode 'A Night Out'. Spooner made only two appearances but is mentioned in other episodes in Series 1. Other tenants occasionally move into the house but never became permanent residents, often appearing only in a single episode. Peter Bowles and Peter Jeffrey were among the actors portraying these tenants.

Frances de la Tour temporarily left the series in 1975, after appearing in four episodes of the second series, because of theatre commitments. She was "replaced" by Gabrielle Rose for three episodes as new tenant Brenda (she also appeared in la Tour's last episode of 1975 "Moonlight and Roses"), whilst Henry McGee also stood in for one episode as new tenant and conman Seymour. Frances de la Tour returned for the final two series.

Richard Beckinsale did not appear in the fourth series due to West End theatre commitments. Eric Chappell wrote some lines into the intended first episode 'Fire and Brimstone' to explain Alan's absence (he had passed his exams to become a doctor) but these were cut when it was decided to broadcast the second episode 'Hello Young Lovers' as the first episode instead.

Eric Chappell defended Rigsby by saying he "was not a racist or a bigot, but he was prejudiced and suspicious of strangers. But he accepted Philip and his only concern afterwards was that he didn't get a leg over Miss Jones."