An Activist Investor is an investor who purchases a not-insignificant stake in a company in order to pressure the board into making a decision that will make that investor a lot of money, generally in a very short period of time. The high-profile investors tend to want to shutter the company completely or to downsize immensely. Basically gut, maximize profits for a quarter or two, and sell.<p>Biggest example is probably Carl Icahn. He&#x27;s well known in the tech world for trying to do these types of things to Apple, Netflix, and Dell. Not sure about the others, but Netflix actually has a Carl Icahn rule that prevents any one investor from gaining too much control. If I remember correctly, Icahn sold his stake almost immediately after the rule was put in place.