Complex sentence: He appeared in three Doctor Who serials directed by Lennie Mayne: as Dr. Tyler in "The Three Doctors", Gebek in "The Monster of Peladon" and Dr. Carter in "The Hand of Fear".
Split into simpler sentences: He appeared in three Doctor Who serials directed by Lennie Mayne. He played Dr. Tyler in "The Three Doctors", Gebek in "The Monster of Peladon", and Dr. Carter in "The Hand of Fear".