Someone who can resolve a difficult problem or situation another person's facing.
Talk to Phil about getting out of that jaywalking ticket. He's your go-to guy for that kind of thing.
This person is often responsible for planning activities and inviting females and other Bros. If a Bro is trying to find something to do, they generally call this “go-to guy”. There can be a maximum of two “go-to guys” in a group. Many times the "go-to guys" is named Dave or David.
I'm board.. what's David up to - he's never bored - he's the go-to guy.