Billionaire investor Carl Icahn resigned Friday from his position on the board of Yahoo!, saying the US Internet giant no longer needed an "activist" director like him, his spokeswoman said.

"I don't believe that it is necessary at this time to have an activist on the board of Yahoo! and currently, my attention is focused on other matters," Icahn wrote in a resignation letter to the board, a copy of which was provided by his office.

Icahn, who was involved in a very public dispute last year with Yahoo! co-founder Jerry Yang, said his departure was effective immediately.