We've talked a lot about Gods and creators in this list, but when you talk about THE God of the Marvel universe, you have to talk about The One Above All. You can tell he's something special because he hasn't done much in the Marvel universe. He has taken the form of a female and male, and doesn't live in time the way we do. For him, everything has already happened and is happening at the same time.
Generally, it seems that The One Above All is a force for good. He even disguised himself as an old woman to give Peter Parker some support. That sounds like the type of God that they taught me about in Bible school. I hope this character remains a mystery, because that's what's so intriguing about a powerful character. We shouldn't even ever have to see their power.