Edward Kelsey (born 1930) played a slave buyer in DW: The Romans, Resno in DW: The Power of the Daleks and Edu in DW: The Creature from the Pit.
According to the DVD commentary for "The Slave Traders", the reason for Kelsey's repeated return to Doctor Who was because Christopher Barry — the director common to all three of Kelsey's stories — liked to draw from a stable of reliable actors for his supporting casts. The commentary further claims that Kelsey is notable as the first non-regular actor to appear with two different incarnations of the Doctor.