Sylvester McCoy has become the seventh actor to play the title role in the British Broadcasting Corp.'s long-running science-fiction fantasy series "Doctor Who." McCoy has taken over from Colin Baker, who assumed the role in 1984. He will join Bonnie Langford as Melanie when the series returns to the BBC this fall. The new episodes will be available for U.S. broadcast early next year. The series, which runs in 54 countries, has been on the air since 1963.