- You may be looking for the Dalek named Beta.
Beta was a Gond scientist who lived under the enslaving regime of the Krotons. Beta resented being forced to accept knowledge, he wanted to discover new things for himself, and he enjoyed experimenting with chemistry, which was forbidden by the Kroton's order because acids were dangerous to them.
Beta and Jamie attacked the Kroton ship's exterior with sulphuric acid, while the Second Doctor and Zoe applied acid to the ship's interior. This action was the proximate cause of the successful end of the rebellion.
Prior to deciding to assist the TARDIS crew, and by extension Thara, he had been heavily courted by Eelek, who was angling for post-Kroton, post-Selris power in a free Gond society. Consequently, Beta's fortunes likely rose in the aftermath of the rebellion, once Thara had become leader of the Gonds.