There is no establishing a learning curve for him. He's able to step right into the action and start kicking intergalactic butt and taking names. These heroes already have a developed history. They were former police, army, etc. and have the skill necessary to get the job done.
That doesn't mean they can't be a fish out of water. William Shatner created the Tekwar series of books that featured Jake Cardigan. Cardigan was a former cop who was framed and put in cryostorage for a few years. When he was finally released, he still had the skills, but the world around him had changed drastically.
If you science fiction is more a epic origin story, then you'll want more of a Skywalker. These characters don't start off with the skills necessary and have to learn them as the story goes on. These could be done suddenly in the form of spells or arcane knowledge or through training and practice.
While they don't have the skills, they often do possess the personality of a hero. They are willing to help out no matter that and are willing to take on a dangerous quest even though they know they are not prepared. The other option is the unwilling hero. He's someone that is thrown into a situation against his will and slowly turns into the hero.