They were really spies, of course, but the tennis cover allowed them to explore many glamorous locales in "living color" (a rarity in tv in those days). They usually spent several episodes in the same locale before moving on -- eight in Hong Kong, five in Japan, five in Mexico. They were occasionally involved with women, but their strongest emotional bond was with each other.
Robert Culp starred in the 1969 sex comedy Bob and Carol and Ted and Alice, plus lots of other tv shows and movies, including Greatest American Hero. He died in 2010, still fondly remembered by gay boomers as the wisecracking secret agent in speedos.