Tumtum was one of the three presidents of Versity City's SGA (along with Millions and Foster). Then he died.
Tumtum was the SGA president who was in charge of the water tower. He and his workers were tasked with making water, drugs, and other various chemicals.
He worked in the watertower pretty much as soon as he could walk. Much like the majority of people that work with rainwater too long, he went blind eventually.
Tumtum climbed up the rank and file (through skill and ruthlessness) to become in charge of the whole operation. Once he was valuable, he was able to get "elected" president and hold on to the title longer than anyone one else (eve Foster).
But he's dead now, so it doens't mean much anymore.
Tumtum died at some point or other. Probably. At the Battle of Lockheed maybe?