Kagark may have been the one to stick with my players, but my favorite was Ra-Jareez, a cat-folk (or Nkosi, or Tabaxi) former space captain/bard that joined the crew during my Spelljammer campaign. Mostly, I just liked talking like a khajiit from The Elder Scrolls, but despite the crew never fully trusting him (and he was a bit of a skeevy schemer), I always intended for him to actually be fairly trustworthy and reliable, i.e. he would never betray the crew, no matter how much they thought he was going to. Ra-Jareez is less competent than he regarded himself and more of a scoundrel than he wants people to believe.
In the end, I like to think he schemed his way back into the captaincy of a ship, after all his debts were paid. Like Brisco County, Jr., he was always looking for the next big thing, but to profit from it, rather than just marvel at what the future holds.