Willard (1971) DVD Region 1. (Playable in North America - The US, Canada, Mexico, etc.) Color.
Starring: Bruce Davison, Sondra Locke, Elsa Lanchester, Ernest Borgnine.
A social misfit, Willard is made fun of by his co-workers, and squeezed out of the company started by his deceased father by his boss. His only friends are a couple of rats he raised at home, Ben and Socrates—and their rapidly increasing number of rat friends. However, when one of the rats is killed at work, Willard goes on a rampage using his rats to attack those who have been tormenting him. (Followed by the sequel Ben, also available on DVD on this site.)