A kerbonaut is the KSP equivalent of an astronaut. Kerbonauts are Kerbals who pilot manned spacecraft, space planes, rovers or any other not probe controlled craft.
Each kerbonaut has two attributes which are shown in meters next to its name in the vessel info page and in the astronaut complex, which show its courage and stupidity. These values affect how the kerbonaut reacts to decouplers decoupling, parts blowing up, and other events. There is a third attribute, Bad Ass, which overrides courage and stupidity. Jebediah, along with a few other kerbonauts, has this flag enabled.
The three starting kerbonauts are Jebediah “Jeb” Kerman, Bill Kerman, and Bob Kerman. More can be hired in the Astronaut Complex, each one having a random name, courage, and stupidity. The surname of any kerbonaut is always Kerman.