I thought the cosmic beings in the Marvel Universe were strong, but...
Anyway: Infinity, Eternity, Oblivion, and Death... but they were defeated (or weakened) at some point. Whatever. Here is the list of Marvel's Cosmic Entities
Also, for Marvel: Living Tribunal "The Living Tribunal possesses virtually unlimited power and absolute control over the Marvel Multiverse."
I assume for DC: The Source. You can click on the link and read its history there as it is long.
I'm sure DC and Marvel created a cosmic being that is responsible for the creation of Amalgam comics but I'm too lazy to look for it right now.