Oguma is the main antagonist of Metal Slug (PS2). He is the last surviving member of an ancient race, which he seeks to save by altering the timeline.
Oguma is a well known businessman and head of the Oguma Corporation, a company that specializes in gadgets of all sorts. He aligns himself with Donald Morden, showing interest in an artifact the general found called Alator. The two joined together to decipher the object, whose technology could create weapons superior to anything known to man. Oguma uses the resources from his company to finance the Rebel Army, which launches a new coup d'etat.
When the two finally unlock the Alator, Oguma betrays Morden and takes the artifact. Oguma reveals he hails from an ever-evolving ancient race, which will self-destruct when they reach their evolutionary peak, and that the Alator was the key to saving his race. The object was actually an information gathering device which recorded human history, intending on finding a perfect timeline, otherwise it is just taken back to the past while the current timeline is erased. Oguma reveals he have repeated this experiment countless times, so the heroes step in to save their timeline.
Oguma activates the Alator, which summons a giant. While Oguma retrieves all the data, the heroes fight the giant, but once they defeat it Oguma's experiment goes awry, as all his data is erased and another giant appears. Oguma is unable to control it, so the heroes are forced to fight it. Failing to save his race, Oguma accepts his fate and thanks the heroes before disappearing.
Somehow, Oguma survived, being last seen giving a data disc to Rumi Aikawa containing the history of his people, hoping that his mistakes can serve as a lesson to humanity.