Gardner Monroe is a living temporal anomaly. He can temporarily bring copies of himself from an alternate future into the present and control them. The difference between Flashback and his summoned future-selves is his future versions wore a differently colored, negative version of his costume.
He shortly associated himself with Beta Flight, Canada's undercover superhuman team. After Department H went under he was rectuited into Omega Flight.
He has not been seen since one of his versions was seen in the House of M reality. Whether this was himself or one of his copies remains to be seen.
Eath 295 - Age Of Apocalypse
Flashback was targeted by Apocalypse as a threat, and sent his chrono-variant mutants after him. It is unknown what happend to him as he is listed as Missing In Action within Apocalypse's files. As seen in Generation Next #1, while Know-it-all was searching for any Time Traveler.
In the House of M reality, Flashback is a member of the Thunderbolts under Baron Von Strucker. He is seen fighting the Kree Soldier Private Genis-Vell, After an unknown anomaly he disappears and his fate is unknown.