Amon Krieg was a former counter-intelligence agent hired by Ari Tasarov to protect his son, Stefan, instead of retiring. He says that as long as the money doesn't run out, his son will be safe as Krieg is the best operative he's ever seen. In Reunion, he fends of the mercenaries of Amanda and instead of leaving Stefan when the money does run out he stays and keeps Stefan hidden. Nikita and Alex find them and take Stefan after he got thrown of a balconny. Tracking them down he kidnaps Amanda and Nikita to get him back. He is about to torture them but gets called by Alex who says she had Stefan. He meets Alex and the two ended up in a standoff before he got called and Ari convinced him to help Division. The two find Stefan and take out the mercenaries guarding him, and Alex saved him when he got caught of guard. As they escaped he shielded Stefan and took a bullet for him. Alex staid behind to keep the mercenaries away and told him and Stefan to leave. At the end of Reunion, he tells Stefan that it's his life so it's his choice as to where they go next. He'll stay with him.
Krieg was highly loyal. According to Ari something had happened to his wife and because his life became his work he had no life to get back to after retiring. Krieg is loyal towards Stefan and kept helping him even without getting paid, going as far as taking a bullet for him. He is serious and constantly aware of possible dangers. After Stefan got taken he was willing to go to extremes to get him back and even wanted to torture Nikita and Amanda to retrieve him.
Even though the original agreement was Stefan would be protected as long as there was money in Ari's private account, after spending so much time protecting him, he eventually thought of Stefan like a son, unable to abandon him, even after Amanda emptied Ari's account.