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. However, Kelsey was the first guest actor to appear in stories with two Doctors.
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