Krona

Krona is one of the most powerful beings in the DC universe "“ in fact, he is so powerful that he managed to jump in the Marvel universe and threaten to destroy it. Only the combined forces of heroes such as Batman, Captain America, Atom, and Superman wielding Thor's hammer and Captain America's shield managed to stop him.

So that says a lot about him.

Krona, a Maltusian just like the Guardians of the Universe, is the strongest of his race. And, as a scientist, he can be called responsible for the creation of the multiverse "“ using a machinery he invented, he managed to catch a glimpse of the beginning of time, an act that creates a powerful explosion that, in turn, shattered reality in infinite parallel universes.

It can be said that his greatest power comes from his thirst for knowledge, Krona being a supreme-genius level intellect. However, this is also his greatest weakness, since he has put even himself in danger in order to gain a bit more knowledge (really, this is a weakness when you put everything at stake in order to be able to find out, for example, how much a soul weights).