Henry Allen

Not sure about this one, but it is by far the best theory out there. Henry Allen from Earth-2 was the one who became a speedster after a particle accelerator went kaboom, but the explosion killed his son, which is why he torments Harrison Wells by kidnapping his daughter. Additionally, his speed only reminds him of the tragic event that took place, as well as the existence of any other speedster, so he decided to eradicate them completely.

Furthermore, Zoom’s eyes are somewhat similar to Henry’s, so this may very well be a viable theory concerning Zoom’s identity. Besides, it would be great for two Henrys, who are fundamentally the same person, to turn out to be complete opposites, due to the difference in the lives they’ve led.