Most of those listed so far are pretty good. I'd add ( though their feats are limited)
Niles Caulder (the chief) who manipulated events ( retconned post COIE) to create the Doom patrol. Created the circumstances in which each of their "accidents" happened and manipulated governments and gov bodies to suit his needs.
Dr Mist ( PRE COIE only) who also manipulated governments and world politics to have his little Global Guardians. he was a LOT less impressive at it post COIE.
Also Kingpin. He wields quite a bit of Weight ( yeah I meant the pun) and influence in MU.
NO ONE has mentioned Thanos ??????
Red Skull would have to rate somewhere in the top 20 surely to god.