Mitt Romney, the former governor of Massachusetts and a candidate for the Republican presidential nomination, has lately found himself on the defensive regarding his work at Bain Capital, the investment firm he helped to launch in 1984.

Mr. Romney’s campaign recently released a television ad in South Carolina — the primary there on Saturday is the next major stop in the Republican nomination process — that painted him as a job creator who, while he was an executive at Bain, helped to launch businesses including Staples, the office supply company, and the sporting goods store Sports Authority.

Officials with Mr. Romney’s campaign are thought to have launched the ad partly to combat the criticism he has faced from fellow Republican candidates who have recently claimed that during his tenure at Bain, Mr.Romney actually oversaw the closing of several failing firms that resulted in thousands of layoffs.

Mr. Romney, who has said that he created 100,000 jobs in the course of his work there, was cast as a “vulture capitalist” by Gov. Rick Perry of Texas in an interview with CNN on Jan. 10.(Mr. Perry has since withdrawn from the race.) Additionally, a short film produced by a committee supporting Newt Gingrich, also a Republican presidential candidate, depicts Mr. Romney as “more ruthless than Wall Street” and alleges that his firm was “killing jobs for big financial rewards.” The film’s accuracy, however, has been questioned by media organizations, and Mr. Gingrich has called on the producers to “edit out every single mistake or to pull the entire film.”