Upton likened it to a boxing match between a heavyweight and a featherweight, a relationship that "oscillated from ardour to hatred, reconciliation and remorse." On 20 March 1977, Sellers suffered a second major heart attack during a flight from Paris to London; he was subsequently fitted with a pacemaker. Sellers returned from his illness to undertake Revenge of the Pink Panther; although it was a commercial success, the critics were tiring of Inspector Clouseau. Julian Upton expressed the view that the strain behind the scenes began to manifest itself in the sluggish pace of the film, describing it as a "laboured, stunt-heavy hotchpotch of half-baked ideas and rehashed gags". Sellers too had become tired of the role, saying after production, "I've honestly had enough of Clouseau—I've got nothing more to give". Steven Bach, the senior vice-president and head of worldwide productions for United Artists, who worked with Sellers on Revenge of the Pink Panther, considered that Sellers was "deeply unbalanced, if not committable: that was the source of his genius and his truly quite terrifying aspects as manipulator and hysteric." He refused to seek professional help for his mental issues. Sellers would claim that he had no personality and was almost unnoticeable, which meant that he "needed a strongly defined character to play." He would make similar references throughout his life: when he appeared on The Muppet Show in 1978, a guest appearance that earned him an Emmy nomination for Outstanding Continuing or Single Performance by a Supporting Actor in Variety or Music, he chose not to appear as himself, instead appearing in a variety of costumes and accents. When Kermit the Frog told Sellers he could relax and be himself, Sellers replied: Being There, Fu Manchu, and continued domestic problems (1979–1980) In 1979, Sellers starred alongside Lynne Frederick, Lionel Jeffries and Elke Sommer in Richard Quine's The Prisoner of Zenda. He portrayed three roles, including King Rudolf IV and King Rudolf V—rulers of the fictional small nation of Ruritania—and Syd Frewin, Rudolf V's half-brother. Upon its release in May 1979, the film was well received; Janet Maslin of The New York Times observed how Sellers divided "his energies between a serious character and a funny one, but that it was his serious performance which was more impressive". However, Philip French, for The Observer, was unimpressed by the film, describing it as "a mess of porridge" and stating that "Sellers