Oswald/Story

The King of Fighters XI
Oswald is a man who is said to be a professional hitman who seems to be in retirement. Ash requested for Oswald to join the tournament based on rumors he heard about him. Since neither knew much about the other, the conditions for joining the team was decided in a poker game; the winner would choose to do what they pleased. Despite having a winning hand, Oswald recognizes Ash's skill and accepts defeat - he introduces himself to his teammates while being brought out of retirement.

It is revealed at the end of the tournament that Oswald joins Ash and Shen Woo to obtain money and the drugs named 'Dragon Pills' (which hint that Oswald is suffering from a disease). Ash agrees to give information regarding the drug to him, explaining that it can only be given to him if he defeats the provider's enemy, Shen Woo. As Ash left Oswald and Shen alone by themselves, a battle between the two took place, the winner of which has yet to be revealed; though the confirmed survival of both Shen and Oswald makes either outcome equally plausible. Either way, Oswald was seemingly out of commission or had decided to not participate in the next tournament.

The King of Fighters XIV
Oswald returns as DLC. His apparent disease is somehow either retconned or seemingly resolved with the existence of Ash vanishing in KOF XIII, and thus it seems he no longer needs the Dragon Pills anymore. Oswald then deems himself to be lucky enough to be free of that burden, and more of his personality opens up in the coming tournament.