The General
The General was the Time Lord military commander who led the War Council, therefore the efforts to defend Gallifrey from the Dalek onslaught in the final days of the Last Great Time War.
In the aftermath of the Fall of Arcadia, he was informed of the War Doctor's appearance there. He was then alerted to a security breach in the Time Vaults, discovering that the Doctor had taken the Moment, the last weapon in the Omega Arsenal.
He was later contacted by three incarnations of the Doctor, the War Doctor with the Tenth and Eleventh Doctor, who revealed to him their plan to save Gallifrey by freezing it before its destruction and shifting it to a pocket universe. The General was sceptical, shocked by the thought of being lost and forgotten in another universe, but with the Dalek fleet closing in, he soon gave the order and "all thirteen" Doctors performed the process together. (TV: The Day of the Doctor)
Behind the scenes
The General was played by Ken Bones, who also provided the Time Lord "Voice" asking the Question, "Doctor who?", in The Time of the Doctor. Although not explicitly confirmed, it can be inferred that the voice asking the Question was that of the General. Indeed, the subtitles on the Blu-Ray and DVD identify the voice as that of the General.
