Need Help About The Fathomless

Hi!! I'm trying to create a Warlock, but I need some help with the patrons. The character, Cathal, is a former pirate. So I think The Fathomless would fit him perfectly from a story perspective. But I couldn't find much information about them on the character sheet creation sites. What would a sample first-level character look like?

I don't recall seeing "The Fathomless" in the 2024 PHB, what is it?

Thank you.  I realize that not everything is 2024 PHB, but then not everyone has non 2024 material, so the only reference is the 2024 PHB.