Rick is too smart for his own good, an otherwise average looking person, he lived on the streets and found his way into the thieves guild to stay alive.  They taught him magic and other forbidden things when they recognized his great intellect but subpar ability to pick a pocket.

Eventually, his good nature won out, and he tried to part from the thieves guild.  Using what he learned from his teachers, he disguised himself, and ran, looking to make a more honest living in adventuring.  Though nothing was able to cure him of the desire for gold and riches that the Thieves guild so expertly taught him, despite his otherwise good nature.  Also, being a half-elf, a thief, and young, he has no respect for law or authority, believing his own mind to be better than any of society's rules.