Michael Oltman (Mikhail Ortmann; English translation) is one of the main characters of the side story Xenosaga: Pied Piper. Though he is not a playable character, he does work under Captain Jan Sauer (later Ziggurat 8) in the 1875th Federation special-ops detachment squad.
At the time of Pied Piper, Michael is 27 years old. He is a talented U.M.N. operator who specializes in overseeing dives (links between a person's mind and a virtual space, or two people's minds to one another). He's the most vivacious of the bunch and often serves as a morale officer for his more serious teammates. He also seems to carry a torch for Meris, and he is constantly getting himself into trouble because he can't say no to her.
His partner is Erich Weber, and the two seem to be very close, despite Erich's secret identity as the serial killer Voyager. As Erich slips away, Michael grows more and more suspicious, until the situation comes to a head and Erich brainjacks Michael in an attempt to protect himself. Unfortunately, he then had to be subdued by Jan and the others, and he subsequently died from the damage he sustained. This is quite possibly Erich's final act before slipping completely into the persona of Voyager.