Mr. Williams is the Coolsville's bank janitor.
Physical appearance
He's a hulking Caucasian male with short brown hair, and a five o'clock shadow.
Personality
He's dedicated to his work, and was rather thoughtful when telling Scooby-Doo to give him a call if he ever needed a janitor. He was so dedicated to the bank that he followed the trail of the sludge monster that robbed it.
History
A Pup Named Scooby-Doo
Season one
He was working late one night at the bank, and he witnesses what's inside the vault stealing the money. His boss, Mr. Buckston, dressed up as the Sludge Monster from the Earth's Core so he could steal all the money and frame it on him. When the Scooby gang was on the trail of the Sludge Monster at the bank, only then when they find Mr. Williams, it made him a suspect. Given the rough appearance of Mr. Williams, as well as the temptation of being around large amounts of money, it made sense that he would try to rob the bank as the Sludge Monster. However, Mr. Williams was found innocent after the gang unmasked the monster as Mr. Buckston, and thanked the gang for exonerating him. (The Sludge Monster from the Earth's Core)