Sigma

Ood Sigma was the personal Ood of Mr Halpern, manager of Ood operations. He was the most important Ood. He dosed Halpern with Hair tonic as he was balding. Sigma travelled with Halpern to Ood Operations. Sigma remained by Halpern's side even when all the other Ood were infected with Red Eye. Sigma led the Doctor and Donna Noble to the the room containing the Ood Brain. There Sigma revealed to Halpern he had been dosing him with a liquid that turned him into an Ood using the hair tonic. Sigma then declared he would look after Halpern. (DW: Planet of the Ood)