Mister Sinister is one of the most complicated characters within the Marvel Universe. Not just because of his long life, but the facts that there are multiple versions of it. For years now, there have been several other Sinister clones running around. Though their goals are the same, they are ultimately hostile to one another for one specific reason: They believe themselves to be the original, while all the others are clones.
Source：https://www.cbr.com/xmen-mister-sinister-clone-weakness/
