The X-Men have some of Marvel's most impressive and memorable antagonists, from the morally-murky Magneto to the monstrous Cassandra Nova. Their modern foe, Orchis, have taken the Sentinel concept to a terrifying new level. Among these villains is Sebastian Shaw consistent thorn in the side of the X-Men for decades. Even when nominally an ally to the heroes, Shaw has proven to be a consistent and constant threat.
Source:https://www.cbr.com/xmen-sebastian-shaw-bad-luck-marvel-comics/