Gregor was abandoned in Kassen and, due to his dubious heritage, was ostensibly left to fend for himself. But many of the folks in Kassen are decent people at heart and a number of the townspeople looked out for the youngster. Often, Fr. Prasst would let him sleep in the Church of Erastil; often Olmira Treesong or Arnama Lastrid would bring him some food from the wilds; often others would leave out some food or clothes that their kids had outgrown. He survived and learned from those who would teach him. His survival, combined with his orcish looks, earned him the nickname "The Roach." As Gregor aged, he began more and more to run with Arnama on her treks, learning the skills of a ranger from her. He recognizes that she is a bit temperamental and not the best of teachers, but he loves the woods and the wilds.
Gregor lived on the outskirts of decent society. Sometimes people would do him a kindness, but they often blamed small crimes on him and worried that he would lead their kids astray (or eat them, if you listen to some stories). Consequently, Gregor has a certain aura of danger about him that interests certain youths. The truth is that Gregor is not much of a rebel at all. He's a fierce believer in Erastil, especially in Erastil's teaching about the virtues of small communities. He's learned to be gruff and to put on a fierce aspect, but Gregor truly loves Essan and the surround areas.
Most folks assume that Gregor will eventually move on from Kassen, that he will seek out some place that will be more forgiving of his heritage and fierce appearance. They are wrong. Gregor nourishes each small act of kindness that enabled him to survive. Kassen is his home, his place. He plans on protecting it, even if the people of Kassen don't fully welcome him.