The life of James Proudstar seems to be partially defined by tragedy. He grew up hardly knowing his older brother, John, but nevertheless held him in high regard, watching him become a local hero. Later, his brother would be recruited into Charles Xavier's X-Men, taking the code-name Thunderbird, but he died on one of his earliest missions. Just before Thunderbird's funeral in the Western Desert, Proudstar stole his brother's body and gave him a traditional Apache warrior's funeral rite. Blaming Xavier for his brother's death, Proudstar accepted an offer from Emma Frost, then the White Queen of the Hellfire Club, to join her team, the Hellions. He took the costume and code-name of Thunderbird in his brother's memory.
Proudstar later sought out Xavier and unsuccessfully tried to defeat the X-Men. Ultimately realizing that the X-Men were not responsible, he dropped his vendetta. Declining Xavier's offer to join his team of X-Men protégés, the New Mutants, Proudstar returned to the Hellions as their leader. Eventually, however, James left the Hellions to return home to Camp Verde.
Years later, during a trip to New York, Proudstar was approached by Cable to join his formative strike-force, X-Force. Proudstar initially refused the offer and returned home to find that everyone on his reservation had been slaughtered and a Hellfire Club mercenary's mask left behind. Vowing revenge, he accepted Cable's offer under the code-name Warpath, hoping that he could later use the team in his revenge. Warpath adventured with X-Force for a long tenure. Over time, he developed his powers to higher and higher levels. He also developed a crush on his teammate Siryn and was instrumental in helping her recover from alcoholism. Proudstar eventually confronted Emma Frost over the death of his people, but she convinced him that it was not the Hellfire Club that was responsible.
After a couple of years, Proudstar left X-Force, after an encounter with a young mutant named Risque. Together, the two wandered the country, and Proudstar was taken in by Risque's seductive ways. Ultimately, however, Risque betrayed Proudstar, drugging him and delivering him to a mutant called Sledge. Sledge later informed Proudstar that a member of his tribe, Michael Whitecloud, had not died in the massacre. Sledge offered to give him to Proudstar for a fee. Proudstar accepted since Whitecloud is the only member of the tribe to know the truth about the massacre. After meeting with Whitecloud, it was revealed that the time-travelling clone of Cable, Stryfe, had engineered the Camp Verde massacre. In order to confront Stryfe, Proudstar had to travel to Hell itself, realm of the demon Mephisto. After a battle, Stryfe wished to switch places with Proudstar. However, the Mephisto's son Blackheart retained Stryfe's soul and allowed Proudstar to return to Earth.
James eventually paid the debt he owed Sledge by traveling to an alternate dimension and freeing the Vanisher who was trapped there. (Sledge's motives for this exchange remain unrevealed.) James then returned to X-Force, where he continued to adventure alongside his friends as simply Proudstar.
After one adventure, X-Force survived being in the center of a Vibranium bomb explosion. The team decided to let the world believe them dead and to use this status to secretly infiltrate and destroy anti-mutant organizations around the world. After half a year of this hit-and-run strategy, they learned of a great underground complex where Wisdom's sister Romany was infecting people with alien DNA to alter the human race. In the final battle, X-Force destroyed the alien complex and was believed dead. During this time, Proudstar began to exhibit strange fluctuations of power, such as the ability to fly, and he seemingly lost the ability to speak. The reasons behind this change have yet to be fully revealed.
Proudstar and X-Force reappeared at a press conference of a new team calling itself X-Force, challenging the team (now called X-Statix) in dispute for their name, although Proudstar and his teammates were ousted, and most of its members went their separate ways. Proudstar went on to join the X-Corporation in its branch at Mumbai, India, and has was later spotted among X-Force once again.
After the events of House of M|M-Day, James relocated to the "198" mutant encampment on the grounds of the Xavier mansion, and has since reconnected with Professor Xavier. Along with four other X-Men, Proudstar, once again using the Warpath alias, joined him on his quest to stop Vulcan from destroying the Shi'ar.