RJ was an orphan who was taken in by HYDRA, trained to kill without little to no morals.
RJ first appeared as a HYDRA assassin, who killed a man in the witness protection program who was speaking to Bucky Barnes (The Winter Soldier). Both of them begin fighting, seemingly being evenly matched. RJ takes out a sword and tries to cut off his arm, but his metal arm only received minimal damage. Bucky takes the chance to knock him out.
RJ wakes up on a motorcycle, with Bucky taking him somewhere, trying to talk to him. Unknown to Bucky, RJ activates a tracker for his HYDRA mentor to find him. His mentor destroys the bike, confronting RJ. To his surprise, his mentor rejects and shoots him. Bucky defeats him, finally convincing RJ to come with him and quit HYDRA.
After spending time together and doing missions, even defeating the villain Spot. Everything seems to be going good, when RJ’s missing father comes back into his life, causing Bucky to feel threatened and scared.
With RJ and his father connecting, Bucky discovers that his father is in trouble with a loan shark. His father attacks him, but then he accidentally hits his head on a dumpster and dies. Bucky hides his body, with his friend, Sharon Carter, advising him against hiding it from RJ.
Eventually, the truth comes out, with RJ being furious at Bucky. He storms out of the house and leaves for good, with Bucky not knowing where he went. We later see that RJ has returned to killing, but now he’s killing the good people instead, seemingly still angry at the Winter Soldier.