Whose Line proved a success when aired on Channel 4, effectively helping to boost the careers of some of its regular performers that appeared during early episodes, including several members from The Comedy Store Players - these included Paul Merton, Josie Lawrence and Sandi Toksvig. At times, the programme also featured a number of celebrities who made occasional appearances during the earlier series, such as Peter Cook, George Wendt, and Jonathan Pryce. While the programme drew from the talent of British comedians, it also expanded to recruiting those from the United States; comedians such as Greg Proops and Mike McShane added considerably to performances, with some episodes in the third and fourth series filmed entirely within New York and thus drawing talent purely from American performers. By the fifth series, several regular performers discontinued their involvement, yet the show was greatly enhanced by the involvement of fresh talent by this time - British comedian Tony Slattery, American comedian Ryan Stiles, and Canadian comedian Colin Mochrie, improved the reputation of the programme and provided more diverse comedy and favorable viewing figures, effectively becoming prominent regulars in episodes.
