John Grey was the father of founding X-Men member, Jean Grey and the husband of Elaine Grey. 
John and his wife were temporarily transformed into demons by the Goblin Queen, a clone of their daughter, Jean.
After the death of her daughter, Sara Grey-Bailey, and possibly her husband Paul, Dr. Grey and his wife Elaine took care of their grandchildren, Gailyn and Joey.
When Operation: Zero Tolerance occurred, John was aided by X-Man, who ironically was his alternate reality grandson, in saving his grandchildrens, Joey & Gailyn. 
John Grey was killed by Shi'ar Death Commandos when they tried to completely eliminate the Grey Genome. 
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