History Eater

The  was a creature the War Doctor fought during the Time War.

Rassilon sent the Doctor and four versions of Asmuth to Estragil, to discover what was causing time distortions. On their way, they fought several Daleks, but Asmuth was hit, and died. The Doctor went on alone, trying to find the source of the distortions. Then, the Doctor found the History Eater, who swallowed an entire fleet of Daleks on his own.

The General arrived, and ordered his army to shoot the History Eater. The Doctor, however, said that he shouldn't do it, because not even the Daleks had a chance against him. The Doctor, the General and his army headed back to the Capitol. (NOTVALID: Bigger on the Inside)

Behind the scenes
Although the name is not given in-game, the authours have confirmed the creature is named "History Eater".