There's been many. I'll give special mention to one from my sci-fi hack and slash canon, now dead and a part of the lore's history.

Howard Oleman, a member of the Wernke Republic's Colonial Defense Fleet. His skills were almost exclusively in diplomacy, and as such, he was an official dignitary for inter-faction affairs. The Wernke Republic is the undisputed largest human empire in the lore, so massive that there's a total of five unique "fronts" in space. Oleman was present on three of them, nearly unheard of for virtually any human being, and impressive for someone in diplomacy. His life was pretty much one adventure after another, and he was resourceful enough to pull through almost all of them unscratched. He knew several big names, also deceased, and was good friends with the strongest commander in the Republic (they died months apart from each other). He was energetic, even upon reaching 300 years of age (when people typically die) and believed in doing as many healthy things as possible. The aforementioned general spent more money than real world billionaires ever gain to extend his biological lifespan, and yet Oleman did none of that and was 50 years older.

The thing that makes Oleman stand out for me is his naturally enigmatic personality and the fact I've used him in a couple dozen solid roleplays that happened well before I joined this site. In fact, he was probably one of the most fleshed out characters I ever had. Alas, I age all of my characters, and so while death is rare in the sci-fi canon due to the fact people in even moderately high positions in life live to be 250-300, Oleman reached 310, and he ultimately had to die. He is not, alas, succeeded by any family, and there's been nobody to quite fill his shoes.