I love idiot fuckboy characters. And I wanted to write a bard. Melissa also needed someone she could be distrusting and immature with.
Hence, Felix.
Honestly, I think I really failed at the fuckboy aspect, as he seems to like to hit on people but never really gets anywhere with them? I don't feel bad about this. I'm not even sure about his sexuality at this point. I think he might be aromantic.
I think I really lucked out with him overall, especially with his friendship with Melissa. They'll never directly acknowledge their fondness for each other, but by the end of Prophecy Failed they trust each other implicitly, because neither is in the habit of lying or sugarcoating or even being nice to the other. Felix was basically the only kind of person Melissa could stand to be around during/after her time in the woods.
Visually speaking, I just reused a one-off character design I liked. His look never really evolved because it was pretty good to begin with.
Felix is the only person intentionally named after someone specific. Felix Leiter is James Bond's CIA BFF when he's not getting mauled by sharks. (I am a big nerd.)