In need of content during the 2007-2008 Writer's Guild of America strike, comedians Jon Stewart, Stephen Colbert, and Conan O'Brien created an elaborate faux feud to attract viewers, which culminated in a mock battle between the three hosts on the set of Late Night with Conan O'Brien. Though perhaps the most elaborate, this was far from the first instance of cross-pollination among late night talk show hosts.
Johnny Carson on Late Show with David Letterman
Jay Leno, soon-to-be host of The Tonight Show, on Letterman
Conan O'Brien on Leno
Jimmy Kimmel on Leno's 10pm show
Jon Stewart on Letterman
Stephen Colbert and Jon Stewart on Late Night with Conan O'Brien