Details from the game:

• Reno is the one who sets off the explosion that destroys the Sector 7 pillar, causing the plate to collapse and bury the Sector 7 slums. He leaps off the tower, is presumably picked up by Tseng in a helicopter, and then disappears from game play for quite a while. It's fairly certain that he was badly injured in either the fight with Cloud, Tifa, and Barret on the tower, or by the leap from it.
• Later in the game, Reno makes what seem to be a number of "mistakes" in finding and stopping Cloud and co. Whether he was acting on his own to spare Cloud (or his companions), or if he was acting on two sets of orders remains unclear. The Wutai side-story (if you convince Yuffie to join your party and take her home to Wutai) points to Reno acting on his own, and that's the interpretation I take.
• Reno acts as Tseng's second-in-command, and takes over as leader of the Turks when Tseng is lost in the Temple of the Ancients.

Fanfiction "canon:"

• Reno is a smartass who shoots his mouth off as often as he does his gun when he's out working as a sharp-shooter.
• His past includes either an abusive childhood, or a life on the streets, or both, which leaves him scarred and haunted.
• He'll hop in and out of just about anybody's bed, and gets written in about a dozen pairings including: Rufus/Reno, Tseng/Reno, Reno/Rude, Reno/Cloud, and even Reno/Elena or Reno/Tifa. ~_~