Diavel

Diabel (ディアベル) was one of the 10,000 players who were trapped in «Sword Art Online» and is the only known beta tester other than Kirito, Argo, and Coper. He also appears in the «Aria in the Starless Night» side story.

Appearance
Diabel had a bronze armor on his chest, shoulders, arms, and shins, with a large longsword on his left waist, and a kite shield on his back. He had long blue hair and blue eyes. His clothes under the armor was also blue.

Aria in the Starless Night
Diabel was a beta tester for SAO. Two months after the start of the SAO incident, Diabel became the leader of the raiding group that challenged the first floor boss of SAO.

Secretly desiring prominence and identifying Kirito as his biggest rival, Diabel takes steps to hinder Kirito from getting the last attack (LA) on the boss monster of the 1st floor. First by trying (and failing) to buy Kirito's sword, and finally by relegating Kirito to the support role of fighting «Ruin Kobold Sentinels», the boss monster's guards.

During the 1st boss fight, Diabel showed great skill in commanding the raiding group against «Illfang the Kobold Lord», gradually wearing down its HP with no losses. But as the boss's HP dropped to critical, Diabel charges forward in a bid to land the last attack himself. Expecting the boss to switch weapon to a Talwar, which was the case during the beta, the boss instead produces a Nodachi along with a completely different attack pattern. Surprised and too late to react to the change, Diabel is struck down by a devastating combo from the boss.

As his HP bar vanished, Diabel asked Kirito to defeat the boss monster and save the others before dying.

Trivia

 * In polish "Diabeł" means "Devil"