Question: which actor has appeared in most carry on films?
Answer: Kenneth Williams (1926–1988) (25 films, and co-presenting That's Carry On!) ... 
Joan Sims (1930–2001) (24) had the longest uninterrupted run of roles in Carry On films, being in all 20 films (excluding That's Carry On) from Carry On Cleo to Carry On Emmannuelle.