"Forbidden Planet" became an instant success, and roles in other MGM films such as "Ransom!" (1956), "The Opposite Sex" (1956) and "Hot Summer Night" (1957) followed. In 1957 he won the lead role opposite Debbie Reynolds in the romantic comedy "Tammy and the Bachelor", which, as a "Chicago Tribune" critic wrote in 1998, made people consider Nielsen a dramatic actor and handsome romantic lead. However, dissatisfied with the films he was offered, calling the studios "a Tiffany, which had forgotten how to make silver", Nielsen left MGM after auditioning for Messala in the 1959 "Ben-Hur". Stephen Boyd got the role. After leaving the studios, Nielsen landed the lead role in the Disney miniseries "The Swamp Fox", as American Revolutionary War hero Francis Marion. In a 1988 interview, he reflected on the series, saying, "That was a great experience, because the Disney people didn't do their shows like everyone else, knocking out an episode a week. ... We only had to do an episode a month, and the budgets were extremely high for TV at that time. We had location shooting rather than cheap studio backdrops, and very authentic costumes." Eight episodes were produced and aired between 1959 and 1961.