Mark Zuckerberg forced his original co-founder, Eduardo Saverin, out of Facebook in 2005, basically because Zuckerberg felt Saverin wasn’t participating in the business as much as he should have. 'TheFacebook' (which it was known as, in the early days of its inception) was formed as a limited liability company under Florida law. In the summer of 2004, Zuckerberg dropped out of Harvard and moved to Palo Alto, California, to work on the business while Saverin graduated from Harvard and moved to New York to work as an intern at Lehman Brothers.
During this time, the two grew apart and had significant differences about funding and running the company. Zuckerberg needed more money and he eventually formed a new company under Delaware law which bought the old company and, redistributed company shares so that Saverin’s portion went from 30% to 24%. The company then went Public and Saverin’s shares were reduced further, to below 10%. They eventually settled everything in the court, leaving Zuckerberg as the head of the company and Saverin very rich.