Kevin Koss has followed in the footsteps of two generations of extraordinarily talented pilots and has been in a plane almost since he could walk. He's most comfortable in properly equipped fighters, but if it flies, not only can he pilot it, he can make it do things no other pilot can.
His past is unexplained, but he is shown to be a better than passing street fighter, proficient in various small arms up to a portable rocket launcher, and well-known enough in the aeronautical industry to garner immediate respect and a free hand whenever he involves himself in situations which only someone with his skillset could resolve.
Ace met Gina Diggers and Cheetah when they stowed away on one of his flights when they couldn't pay for transportation. He found them by accident and decided to continue to take them where they wanted to go. As a show of gratitude, the two adventurers split the treasure they found upon reaching their destination. Ace and the Diggers have been great friends ever since.
Despite his friendship with Gina, Kevin started going out with her then-arch rival Penny Pincer. He had started seeing her shortly after Gina and Penny first teamed up. What has occurred since then is a serious relationship between the two with Penny working toward getting married, and Kevin getting used to the idea while sidestepping her less than subtle attempts. She has worn him down to the point where he rarely corrects her anymore when she calls him Kevin in public.
They had some issues caused in part when another woman set her sights on Kevin, "Skippy" the Premier ace of the mercenary organization Night Flight. Skippy has more in common with Ace in regards to flying than Penny does, and believed this made her the better choice for him. Penny feared that she would lose Kevin to her and this is where the issue came from. The situation came to a head when Skippy forced Ace to give his word to marry her by threatening to kill hostages after a failed attempt to take over Night Flight's flying fortress the Gull Wing. Penny Pincher then challenged Skippy to an dog fight for Kevin Koss. Whomever lost would "ditch" Kevin and move on. Skippy accepted and it would have been an easy win for her except she had to break off to defend the Gull Wing. It cost her both her plane and the match against Penny, who got a free pass from Night Flight for assisting in the rescue of the Gull Wing. Skippy is leaving Ace to Penny in the mixed belief that Penny does love Ace but she can just be patient that Penny's dangerous lifestyle will end with her being killed leaving Ace to Skippy.
Kevin was conflicted mostly in part because Skippy has been shown to be extremely devious in her plans to get Kevin alone just to give notice that she loves him. She almost worships the skies he flies through and has shown him that she can fly fighter craft AT LEAST as well as he can. On his deciding to and finally getting married to Penny Pincer these feelings have apparently been resolved. Currently as of this writing Penny finally convinced Kevin to propose, and the two have married and are on a "working" honeymoon.
To date - Kevin Koss has flown everything from workbee-type shuttles to FTL-drive starships with rotor-craft and transforming fighter jets in between. He is hideously rich and supports a stable of tens of aircraft with his buying more as he has time for.