Activist hedge fund firm Elliott Investment Management has succeeded in its demands for change at NRG Energy, with Mauricio Gutierrez leaving the company after being named as CEO eight years ago, and spending a total of 19 years with the company, according to a report by MarketWatch.

The company's shares rose 0.9% into record territory in premarket trading on Monday, after news of Gutierrez's departure broke.

The company also announced that it would be adding four independent directors to its board, as part of a cooperation agreement with Elliott, which began agitating for Gutierrez to leave in June saying it believed he had lost the "lost the confidence of the core investor base."

Chairman Lawrence Coben has been appointed as interim CEO while the company finds a permanent replacement.