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 of Kelsey's three stories — liked to draw from a stable of reliable actors for his supporting casts. The commentary claims Kelsey is the first non-regular actor to appear with three different incarnations of the Doctor. This is incorrect as Dallas Cavell, Walter Randall and Bernard Kay had already appeared with the first three Doctors.