Abraham White was the co-founder of the Threshold.
White met the Pariah when it crashed on Earth. When the Pariah offered White power and immortality, Abraham accepted and joined with the Pariah. The duo later created the organisation known as the Threshold.
White died when the Eighth Doctor destroyed the Threshold base on the Moon by destroying a Threshold device known as the Eye of Disharmony. (COMIC: Wormwood)