Rapper MC Hammer is an angel investor, social media guru and early adopter of now ubiquitous tech start-ups. One of the first users of both Twitter and YouTube, Hammer has been called "a tech visionary" by close friend and legendary angel investor Ron Conway. He's an investor in buzzy mobile payments company Square, dance-oriented social network DanceJam as well as Bump Technologies, which lets users share contact information by bumping their smartphones together. Last month, Hammer also announced WireDoo, a so-called relational search engine that he's involved with. --Written by Olivia Oran in New York. >To follow the writer on Twitter, go to http://twitter.com/Ozoran. >To submit a news tip, send an email to: email@example.com.