Nothing certain is known about Tank Man's background, other than that he was trained and brainwashed by his government as a super-soldier and was made a member of the Americans.
Major Story Arcs
Under the command of Dr. Jacob Krigstein, the Americans were sent to Singapore to find and destroy the baby Jenny Quantum, the spirit of the 21st Century. Tank Man gladly did his part - at one point vaporizing an entire maternity ward on the off chance that one of the babies there was Jenny Quantum.
When the Authority arrived to battle the Americans, Tank Man went up against Midnighter. Tank Man appeared to have the upper hand for much of the fight, until Midnighter began asking Tank Man whether he felt that anything he did as a living weapon would be worth it, and he eventually was able to persuade Tank Man to abandon his villainous role. Tank Man pulled Midnighter out of the rubble, hugged him, and then gave him his helmet as he walked away from the fight. When asked why he didn't kill him even after this, Midnighter simply responded, "Why bother? He's already shattered into a thousand pieces."
After the hostilities between Dr. Krigstein and the Authority were peacefully resolved, Tank Man sent Midnighter a letter, thanking him for helping him sort out his life. Now going by the name Jose Delgado, Tank Man explained in his letter that he'd abandoned his life as an evil super-criminal and was now a vacuum-cleaner salesman in Tuscon, Arizona. He'd also married a woman with six children from previous relationships, and the eight of them planned to move to Dr. Krigstein's New Indonesia to start a new and happy life together.