Mega Man Unlimited/WMG

Bass is the one responsible for kidnapping Dr. Wily and stealing his robots.

Just think about it: who else would go through all the trouble of doing all that? When you consider that Bass didn't get the chance to fight Mega Man for a while, it seems pretty logical that he'd have to do something pretty extreme to get his attention. So what better way to do that than taking over Dr. Wily's army of robots and cause a world-wide rampage? The proof is there, too; in the older version of the intro sequence, Wily's kidnapper's eyes are shown near the end of it and they're red (which, of course, happens to be Bass' eye color), not to mention that he's clearly goading Mega Man into stopping him. Finally, he is present on the game's official cover and has a bigger presence than everyone else on it.