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; while the red-eye Ood had been 'contaminated' by the Ood Brain's anger, Sigma had become the focus of the brain's patience, patiently transforming Halpern into an Ood himself. Sigma declared that the Ood would look after Halpern. As the Doctor and Donna departed, Sigma assured them that they would always be remembered as friends of Ood-kind, and would have a part in the song for as long as the Ood existed. (DW: Planet of the Ood)