Original Valiant Universe (1991-1996)
Peter Stanchek realized he was different when his powers started manifesting. He saw an advertisement for the Harbinger Foundation which promised to help people like him. He met the head of the foundation, Toyo Harada who was himself a Harbinger. A Harbinger is a person born with psionic powers. Harbingers have many variations of this power and it manifests differently for each person.
Pete and Toyo were both Omega Harbingers, which meant they were the most powerful and could use their powers in a variety of ways. This fact is what got Toyo interested in Peter. At first, Pete trusted Toyo, thinking he would help him. But later when Pete found Toyo was responsible for the death of his best friend, he set out to stop Toyo.
Along the way, he began to build his group which would become known as the Renegades. The group consisted of Pete (codename: Sting), Kris Hathaway, Charlene Dupre (Flamingo), John Torkelson (Torque), and Faith "Zeppelin" Herbert (Zephyr).
New Valiant Universe (2012-current)
Pete in the new Valiant Universe is a bit of a darker character. When we first meet him this time, he's on drugs to keep his powers at bay and on the run with his friend Joe. He meets up with a childhood friend of his, Kris Hathaway, but she wants nothing to do with him. Pete uses his powers to make her fall in love with him and supposedly rapes her as well.
The Harbinger foundation finally catches up with him. Joe and Kris are taken away from him. His control over her broken, Kris realizes what Pete did and hates him for it. Toyo Harada takes Pete under his tutelage, knowing that he has to keep the boy close because Pete's power is so great.
Pete doesn't fit in well at the Harbinger Foundation and is constantly getting into altercations with the other psionic-powered teachers and students alike. The turning point for Pete is when he's asked to use his power to activate a girl named Faith Herbert. The attempt almost kills her and fails to give her any powers. Pete learns that many students do not survive the activation process and Toyo is ok with this.
Pete escapes the foundation and finds his friend Joe is dead. He finds that Toyo manipulated the events that led to Joe's death. Pete tries to take on Toyo and his fellow Harbingers but is almost killed in the process. It is only because of Faith (who ended up having a delayed activation) that Pete is able to escape.
Major Story Arcs
This was Valiant's first massive crossover and it pitted the entirety of the Valiant Universe at the time against Erica Pierce (aka Mothergod). She sought to remake time in her image. This story brought the Renegades to The Lost Land, a place outside of time. Kris was pregnant when they arrived and the battle lasted for months and she eventually had to deliver the baby in the middle of the war. Pete found out the baby was Torque's (who had been killed before they entered The Lost Land). Even though it hurt him at first, he and Kris worked through it. It was then revealed that the baby was actually Magnus: Robot Fighter whose adult version was busy fighting in the Unity War.
When the group was zapped back to present day, they continued their fight against Harada. This culminated in a huge showdown between Toyo and Pete which left Harada comatose and Pete supposedly powerless. The group disbanded and Flamingo stayed with Pete.
Later, Pete resurfaced as The Harbinger, an armored, brainwashed servant of Harada, hunting down new rogue Harbingers. It is only when the mysterious being known as The Visitor appeared that Pete was finally stopped. The Visitor was revealed to be an alternate version of Pete. When an alien invasion threatened Earth, Pete, The Visitor, and a newly-returned Harada are forced to band together to stop it. When the threat passed, Pete warns Harada to leave him and Flamingo alone.
Acclaim Comics (1996-2002)
After Acclaim bought Valiant Comics, there wasn't much of a presence for Harbinger other than a one-shot book called Harbinger: Acts of God.
New Valiant Universe
Faith seeks out Kris and after brining her to Pete, Kris confronts Pete about what happened between them. She decides that despite what happened, she should help the others out there that have been affected by the Harbinger Foundation. The group sets out to recruit more members and they find Charlene Dupre and John Torkelson.
The group is chased by the P.R.S and after they manage to escape, they lay low under the radar, using their powers to rob banks, steal cars, and wipe memories in order to continue on. Monk gives Peter visions for a new mission that he must save captured psiot kids.