Time Sentinel
Time Sentinels were responsible for maintaining the scribbled timelines on the Axis. They had rounded heads, and their skin had various colours, including blue, red, white, (COMIC: Old Girl) and black. (COMIC: The Good Companion, The Tides of Time, et. al.) They were able to display images and symbols on their heads, including several incarnations of the Doctor and his TARDIS.
The Time Sentinels were present on prehistoric Gallifrey, where they threw time sensitives into the Untempered Schism. (COMIC: Old Girl)
The Time Sentinels later engaged in a kind of civil war caused by the rogue Aspect Red's attempt to take control of the rest. During this event, Aspect Blue referred to a now departed former lone agent, Aspect Black. (COMIC: The Good Companion)
The Doctor stated that he had seen something like them a long time ago, and he had believed that they were Matrix agents. (COMIC: Old Girl)
