- You may be looking for the Silurian.
Kestral was a Zygon warlord who, with Anktra, planned to carry out a traditional duel on the planet Shontaa. This involved fighting to the death using a variety of host bodies. This duel was observed, however, by the Fourth Doctor and Leela, who were on Shontaa for a picnic. The Doctor, realising that the Zygons had the hosts they were mimicking locked up, found the Zygon ship and freed the prisoners.