How it happened (with apologies to Kurosawa)
Version 1) After consulting the tarot, the high chancellor of the writing congress stood up in front of the auditorium where the eminent researchers working on the Warhammer project had gathered. He praised the field researchers, the dousers and the archaeological team for their long efforts and reviewed the warpstone papers over the next two hours. There was still some debate among those who still tried to reconcile their work at CERN with that of the alchemist team, but it was the ancient Chinese medicine delegation who offered a subtle, but highly clever compromise. It was then put to the vote by Ouija board, swearing on a copy of Einstein's General Relativity and after nearly two decades of hard work warpstone was added to the Warhammer canon which would be published later that year.
Version 2) The writer emptied his beer and lit another cigarette, on the shelves were the works of Moorcock, Tolkien and a pile of 2000AD comics, while VHS tapes of Mad Max and Hawk the Hunter were played alternatively. He was furiously punching away at the typewriter and talked out loud to himself. "Transformation stone ? No, Mutation stone ? sounds even worse …" His eye drifted over an issue of Slaine. "Warp stone … Yes Warp stone, which glows a … sickly yel- no green !!!"
Version 3) And lo, there was a heavenly light and accompanied by celestial choirs the Divine Warhammer tome materialized in the GW offices.
Version 4) Some say he wrote all the editions of Warhammer, but doesn't know how to play it, all we know he's called the Stig.
Version 5) Warhammer is the codename for a CIA mind-control experiment started in 1957 to prepare our world for a grim future where there is only war.
Version 6) Rick wondered briefly how a whale could have fallen from the sky in the middle of Nottingham forest, but among the remains he found mostly really bad Vogon Poetry from a period where nobody even tried and Beatnik Free-form poetry was left to run rampant until it managed to set fire to several important things and was subsequently locked up on an abandoned island and the key thrown into the nearest sun. Alongside Rick found a slightly out of date version of the Interplanetary Hopscotch, Conkers, Tiddlywinks and Mass Genocide Guide with the name of the previous owner "Bob" messily written on the side of the only vaguely tasteful cover, which is totally unlike the back cover which to this days is held up by the Desktop Publishers Guild of Gamma Reticuli Seventeen as the Holy Grail of Desktop Publishing. Rick looked left, looked right, crossed out the name and in his haste wrote Rikc and sold it for a few quid and a blister of free figures to Bryan who happened look for a set of rules but couldn't recognize rules if someone slapped him into a permanent coma with a full binder of Advanced Squad Leader extensions.
Pick your version …