Lucille Ball was actually a card-carrying member of the Communist Party. She also later spoke out on behalf of blacklisted communists, but was eventually forced to testify herself and disavow her past connections.

EDIT: Her defense of blacklisted communists is highlighted in the movie Trumbo, about the writer Dalton Trumbo who was blacklisted for being a communist and won Academy Awards under an assumed name until Exodus and Spartacus helped break the blacklist. Bryan Cranston plays Dalton Trumbo, and it’s a decent movie that you all should watch. Here’s a great clip from that.