Doctor Alistaire Stuart and his sister, Brigadier Alysande Stuart, were the founders of the Weird Happenings Organization (W.H.O.), a group that investigated paranormal activity.
They investigated a mysterious train from an alternate Earth which had appeared in the place of another, carrying an alternate Nazi version of Moira MacTaggert. This led him to meet the British superhero team Excalibur. Attempting to return the train's passengers to their proper reality, Alistaire and Excalibur accidentally ended up traveling through various realities of the multiverse, searching for a way home.
The Excalibur member Shadowcat developed a crush on Alistaire of which he seemed blithely unaware, while he found himself attracted to Shadowcat's teammate Rachel Summers.
Some time after their return from this adventure, Alysande was framed for leaking state secrets to S.H.I.E.L.D. and then killed by Jamie Braddock. S.H.I.E.L.D. director Nick Fury met Alistaire at the funeral and told him that his sister was framed. Alistaire found out that the R.C.X. agency had framed Alysande. W.H.O. was dissolved and Alistaire found his government contract transferred to R.C.X., but with Excalibur's help, R.C.X.'s corrupt leadership was stopped. Alistaire stayed on to help the new regime look after the mutated Warpie children left in their charge.
Shortly afterwards, Black Air began its rise to power as a government agency. Black Air seized the Warpies for experimentation, and struck a deal with the London Hellfire Club to arrange a coup. Deciding Alistaire knew too much, they targeted him for assassination and he fled to the U.S. He contacted Excalibur from the X-Mansion, and returned to the U.K. under their protection. Using the information he provided, Excalibur thwarted both Black Air and the Hellfire Club.
Alistaire was asked by the British government to reorganize all of the U.K.'s disparate government organizations handling paranormal affairs into a single Department under his leadership. Later, after Alistaire transferred to MI-6, the Department was renamed MI-13.
He is a scientific genius, mathematician and engineer, and well-read in philosophy, mythology and archeology. Before his sister's death, the two had an almost telepathic link, and he could sense when she was in distress.
Alistaire possesses the normal human strength of a man of his age, height, and build who engages in moderate regular exercise.