Mueller was first elected village president in 1993 and he had a long history of public service before that.
Mueller had also battled a type of bone marrow cancer for four years. His colleagues say he seemed to be winning that fight.
But two weeks ago, his health took a turn and he was hospitalized. Four days ago, tests revealed that he'd contracted west Nile virus, and early Saturday morning, he died.
"He was very outspoken," said Greg Gron, Lombard Village Trustee. "Big leader, in the front of the pack, and he made sure whatever he did was for the Village of Lombard.
"He was just an all around nice guy," said Mike Ciavarella. "If I had to put it into a few words, I'd call him a gentle giant."
Mueller had devoted two-thirds of his 76 years to civic service, the last 19 as Lombard's village president. He had planned on running for another term.
Where and when he contracted West Nile is unclear. It is a source of concern in his village and other communities where the presence of mosquitoes has been far less noticeable this summer.
"I've been outside quite a bit, both my boys play travel sports," said Barb Flint. "I haven't really noticed any."
But they're there. A note posted last month on the Lombard Village website says, "Although the overall mosquito population is down, there has been a dramatic increase in the number of Culex mosquitoes and positive mosquito samples for West Nile Virus."
Saturday night, bunting was up and the village flag flies at half staff in Lombard where a generation has known but one village president.
But as a leader on several boards and commissions, Mueller's reach extended well beyond his hometown.
"You always knew where you stood with him," said Naperville Mayor George Pradel. "A man of convictions, and he was a leader from the beginning, and when he said something, he followed through with it."
There have been 11 reported cases of West Nile Virus in Illinois, nearly all in Cook and DuPage counties. That number will grow, as the reporting process itself takes time.
Funeral services for Mueller are pending.