"Give me a thousand orphans, a hedge maze and enough cheese, and I can ..."
Doctor Getwin Mittelmind is a mad social scientist, one of the Castle Heterodyne inmates, and a softie; he that back during his research days he even let the children out of their experiment tanks for Christmas.
Mittelmind in Castle Heterodyne
He is Fräulein Snaug's boss and protector (though whether he's protecting her or protecting everyone else from her is an open question at present). Rendered somewhat living impaired for a little while due to his heroic resistance to a vicious marshmallow gun assault. Fortunately, Snaug has been fully trained in his repair and revivification and is able to get him jump started in a jiffy -- Junior Scientist Lightning Kits can be so useful.
This incident reveals that he is part machine (he says that everyone is merely Professor Mezzasalma, Mittelmind has "died" several times in the past while within Castle Heterodyne, but has always been revived by Fräulein Snaug.). The extent of these modifications is currently unknown, though we do know there is a pulse cannon built into his chest (which, of course, kills him every time he uses it) and a backup power source to thwart death trauma-induced memory loss. According to
He helps construct a new Von Pinn/Otila,  willingly assists Agatha in her repair of the Castle, (re)survives the experience and is among those prisoners who are released after she is officially proclaimed as the Heterodyne. When the Doom Bell is to announce her ascension, his technically-dead status renders him immune to the Bell's effect.for
He then joins Moloch Von Zinzer's Roving Band of Heroic Repairmen; while in the process of his new duties, he and Mezzasalma enthusiastic admiration of Tarvek's Sparky resource-management style (possibly to Tarvek's dismay..) Along with the rest of the Repairmen, he is presumably trapped in Mechanicsburg when Baron Wulfenbach drops into the city and activates his Take-Five Bomb, but there has been no "in-person" confirmation of this.
We learn the good doctor's first name when he introduces himself to Agatha; he also adds the fact that he got his PhD at the University of Vienna. Later, during the above-mentioned revival scene, when he shows his supposed memory-preserving battery to Moloch, the latter man notes that the object is corroded and was dead for years. Mittlemind shrugs off this inconvenient fact with his usual level of cheer and continues on, seemingly none the worse for wear. Later he shrugs off existential despair induced by the Doom Bell due to thinking himself (and being) already dead.