Dr. Mark Williams, played by Richard Denning, is a character in the film Creature from the Black Lagoon.
He funds the expedition to the Amazon for Dr. David Reed and Dr. Carl Maia. They are accompanied by Kay Lawrence and Dr. Edwin Thompson as well. The purpose for the expedition for Reed and Maia is purely scientific discovery, but for Williams, it's financial. They charter a boat named Rita, captained by the scruffy Lucas.
Before long the Gill-Man takes notice of Kay who is swimming in his lagoon and he follows Rita, killing those aboard one by one in order to get to Kay.
Eventually Kay is taken by the creature to a subterranean cave where Maia, Reed and Williams confront the creature and rescue Kay.