Disagreements arose between Lincoln and Haisman with the BBC in 1968 over a serial introducing another new monster, "The Dominators", leading to the writers' departure from the series and the retirement of the Yeti as antagonists. The Yeti have since appeared infrequently in flashbacks or cameo appearances. One did have a part in the 20th anniversary special "The Five Doctors". They also appear in the 1990s "Virgin Missing Adventures" novels and the 1995 Reeltime spin-off production "Downtime". The Great Intelligence has since returned in Series 7 of the revived series, portrayed by Sir Ian McKellen and Richard E Grant, without the aid of its Yeti servants.