Creeper

Creeper is a former class A psychic villain who used to slowly torture and twist a mind into self-destruction. He vanished approximately seven years ago and has not been heard of since then.
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Creeper arranged for the abduction of Maria Hill. Later, he toyed with her mind and turned her into the villain Black Emerald.
When Black Emerald discovered what Creeper had done, she turned on him so suddenly that he never had a chance to resist, and he died in horrible pain.