- "I'm the owner of Gold Saucer. The name's Dio."
Dio is met when the party first enter the Gold Saucer, looking for clues for Sephiroth. Talking to Dio is optional, but he can be met outside the Speed Square and asks Cloud about the Black Materia. This is the first time in the game the Black Materia is mentioned, and Dio tells that a "boy about Cloud's age" asked him if he had it, but Dio had no idea what he meant. Dio reveals further that the boy who asked him this had a black cape and a tattoo #1. Dio tells Cloud to stop by his collection at the Battle Square before making his leave.
After recruiting Cait Sith into the party they head to the Battle Square to find its employees slaughtered. Dio enters the scene with security guards and blames the massacre on Cloud's group, who are sent down to the Corel Prison. Down in the prison the party find out the true culprit of the events and return to Gold Saucer. Dio congratulates Cloud via letter for having won a chocobo race and gives the party a buggy as an apology for throwing them into the prison as innocents. In a post script of his letter Dio mentions of having met Sephiroth and suggests Cloud try and get his autograph, as this Sephiroth person seems very popular among "boys of your age".
Dio has a museum of collector's items near the Battle Square, one of which is the Keystone. After the events in Rocket Town the party go looking for the Keystone, but Dio is reluctant to give it to Cloud. Dio agrees to give it to him if he fights a round in the Battle Arena. No matter how well the player fights, Dio will award the party the Keystone, but if the player wins all eight rounds, Dio is impressed and will reward the party with items.
After obtaining the Ultima Weapon and the Omnislash Limit Break manual and the W-Summon Materia from the Battle Square, the player can enter special battles at the arena. Some of the random rewards earned from completing the special battles more than once are Dio's autograph and Dio's diary key items, but these items have no function in the game. In the International version of Final Fantasy VII the player has a bonus disc that shows close-up images of all items, where the player can actually view these key items.
"Dio" is Italian for "God".