Who he was
A pipefitter from Lockport, Illinois, who went collecting on his weekends. In the 1950s he found the first Tully monster. Every one that anyone has ever found came out of the same coal pit in northern Illinois.
What happened next
He carried his lumps into the Field Museum in Chicago, expecting to be told what he had. Nobody there could tell him. They could not match it to any group of animals at all. So the staff called it Tully's monster, and the name stuck.
The scientific name
In 1966, the Field Museum scientist Eugene Richardson gave it a proper Latin name: Tullimonstrum gregarium, Tully's monster, the common one. He did not try to place it in any group of animals. Sixty years later, nobody has managed that for certain.