Spike Lee character from Lee's 1986 film
She's Gotta Have It, but more known for a series of
Nike commercials with
Michael Jordan in the late '80s and early '90s.
In the movie, Blackmon is one of the three men battling for the attention of Nola Darling. Blackmon is a bike messenger from Brooklyn who talks wayyyyyy too fast, wears oversized glasses, and has several catchphrases (perhaps most notably "please baby please baby please baby baby baby please!").
However, it was the series of Nike commercials for Air Jordan sneakers that is the lasting legacy of the character. In the commercials (which Lee also directed), Mars is like a puppy dog to Jordan, jumping around, speaking a mile a minute, when around his idol. When watching Jordan play basketball, Mars theorizes "it's gotta be the shoes" as an explanation for why Jordan can jump so high.
The series of black and white commercials ran from 1988-1995, making "it's gotta be the shoes" the catchphrase of a generation, helping Nike dominate Reebok and other competitors in the sneaker wars, and launching Spike Lee's career.
However maybe most notable was Blackmon's effect on the advertising industry. The Blackmon/Jordan combo was extremely successful and showed that African-American pitchmen can sell products in Peoria, Illinois as well as in Harlem. It also helped establish Jordan as the dominant product pitchman of the '90s (Gatorade, Hanes, etc etc).
Lee explained the origin of Mars Blackmon on ESPN.com:
"Mars was really from my imagination. I had asked my grandmother for a name, and she had a crazy uncle named Mars once, so that's where that came from. But I never met anybody like that character. All from imagination. The bike messenger, hoop fan, seer, who was "kinda small," so Nola Darling could dog him, but who loved the Knicks, Bernard King's game. Probably a lot of Mars was me ..."
With Jordan retiring (for the final time?) at the end of the 2002-2003 season, several of the old Mars Blackmon commercials have aired. Additionally, Lee and Jordan filmed a brand new commercial, where Mars tries to confirm whether his hero's really retiring.
Sources:
http://www.adweek.com/brandweek/headlines/article_display.jsp?vnu_content_id=1867156
http://espn.go.com/page2/s/questions/spikelee.html
Personal memories/knowledge
http://www.alternet.org/story.html?StoryID=13801