Being a general collection of events to take place before UXM #1, and which can be sensibly dated via comparative dates from various issues.
1935: Charles Xavier is born to Brian and Sharon Xavier, workers on an American nuclear project never revealed to the general public.
1945: The Trinity nuclear test at Alamogordo on the 16th of July kills Brian Xavier.
1946: Sharon marries Kurt Marko - also at Alamogordo, and blamed by Charles for his father's death - who then moves into the Xavier family home.
c1948: Kurt is killed in a lab accident. Soon after, Xavier discovers his psychic powers.
1953: After joining the army, Xavier (along with Kurt's son Cain) is deployed to Korea.
1957: Ororo Munroe is born.
1958: Jean Grey is born.
1961: Bobby Drake is born.
1962: Xavier meets both Erik Lensherr and Gabrielle Haller, the latter of whom will one day bear him a son.
1964: A crewman is washed from the deck of the trawler Mary D and finds a golden egg on the sea-bed; this rapidly hatches into a hominid girl her finder names Marinna. Piotr Rasputin is born.
1968: Xavier faces Lucifer in Tibet, in a struggle that costs him the use of his legs.
1969: Ororo Munroe gives up her life as a street-thief in order to follow a strange compulsion drawing her to the Serengeti. Katherine "Kitty" Pryde is born.
1972: James Hudson learns his mechanical suit design is to be used by the US Army in Vietnam; he responds by destroying the blueprints.
1977: Xavier founds the X-Men.