Doctor Maxis worked with his assistant, Doctor Edward Richtofen at the Der Riese facility near Breslau. He worked on creating Zombies and Teleportation Devices. His assistant helped him with this and Richtofen created weapons (Wunderwaffe DG-2). It is possible that Maxis was in charge of the whole operation, but it is unknown who actually was. One of the things Maxis would do was to perform experiments and tests though many of these failed.
It is likely that he could be the "Doctor Max" in the radio message in Shi No Numa, with the American in the message having misnamed him.
Doctor Maxis was working on an experiment that involved his daughter's dog called Fluffy. He attempted to teleport Fluffy, but when he did, the plan failed. Fluffy was teleported, but not to the mainframe. She teleported back inside the Teleporter from an electrical force, most probably the ball of electricity players see Hellhounds spawn from. Maxis demanded the door to be opened, but Edward advised him not to. When they opened the door, Fluffy had transformed into a Hellhound. Samantha came running through, asking her daddy what he had done with her dog. The Hellhound began to try and attack, and began to destroy the room. This caused chaos, and as Maxis tried to calm his daughter down. Edward exited and locked the door. Maxis told him to open it, but Edward disobeyed him, and it is presumed he and Samantha were killed. Further evidence suggesting he is dead is one of Richtofens quotes, "Maxis would of been proud" and "I wish Dr Maxis were here to see this".
In the Der Riese room with the Trench Gun, there are pictures of Zombies and Hellhounds and also a blackboard. There is writing on it saying 'levels 5-8 must survive'. One of these levels is when Hellhounds first appear, suggesting that it is referring to them. Also, 'Edward, i know it was you' is written on it. This could have been written by Maxis or maybe by the ghost of Samantha.This suggests that Edward had always planned to set the Zombies loose, instead of just testing on them.