Ben Cooper, Inc. was an American company that manufactured Halloween costumes. The company stayed open from the 1930s through the 1980s, and their costumes were absolutely ubiquitous in the 1950s to the 1970s. If you weren't wearing a Ben Cooper costume, you probably knew a half-dozen kids in school who were.
The company was founded in 1937 by Ben Cooper, a guy who'd got into the theatrical costume biz and designed costumes and sets for the Cotton Club and the Ziegfeld Follies. Live theater was taking a hit during the Depression while Halloween was becoming more popular, so he decided to start selling Halloween costumes. He acquired a company called A.S. Fishbach, Inc. because they had a license to make costumes for Disney characters. (The two companies officially merged at the end of 1942.)