Master of Gasses
Vapor can manipulate the air to create volumes of different gasses, including laughing gas, knockout gas, and pure hydrogen which can then be ignited.
Vapor began his career as a supevillain named Killer Fog, teamed with his then-wife Disc Jockey (now known as Stiletto). He was a reluctant villain, hen-pecked by his dominating wife.
He managed to escape her control only to fall under that of another supervillain, UltraMegaMan. Thrown together with a ragtag bunch of powered and semi-powered criminals, Sid and Graviton became friends. Graviton took Sid under his wing and, once they were free of UMM, invited him to join the Guardians.