Fredrick is a rugged but clean, bounty hunter. Think Stridder, just less pretty.
After the killer was delivered mercy and his path was righted, Fredrick was discovered by Lucius and brought to Amber. Having just learned that his parents were not his real parents and not learning who his parent is, he was very much adrift.
He wandered shadow for awhile, and with nothing else to do, he continued to Dispense Justice, but on a grander scale. After a couple decades he became disillusioned and decided to start working on just one shadow at a time. After just a couple years of work here he was called back to Amber and his life seamed to gain much purpose in one swift stroke.
There was much work that he could do here in the Amber, much work indeed.