Lawrence Lessig is a law professor at Harvard University and a board member of the Electronic Frontier Foundation. He also founded Center for Internet and Society, a left-leaning think tank. He is a proponent of so-called "copyleft" licenses such as Creative Commons (made by Lessig) and the GFDL used by Wikipedia.
These licenses have succeeded in making many works more widely available for the public. But as discussed at Conservapedia:Copyright, "copyleft" licenses can mean that those responsible for creating content have fewer rights and have no recourse if their work is used by others for purposes that they disagree with.
Lessig has properly argued that over-the-top extensions on copyright laws, such as the never-ending extensions on Disney's copyright in Mickey Mouse, violate the First Amendment. The Supreme Court has ruled against other claims made by Lessig that current copyright law was unconstitutional.
Lessig is also one of the board members of the Free Software Foundation which promotes the "copyleft" ideology.