FLORIDA CITY, Florida (Reuters) - A top aide to President Barack Obama who has managed much of his schedule, planned events and helped choose staff and appointments will leave the White House in early May, a White House official said on Saturday.

Alyssa Mastromonaco, Obama's deputy chief of staff, first joined his team when he moved to Washington as an Illinois senator in 2005.

"Every event the president's ever done, every trip he's ever taken, every decision that he's ever made, she knows about and remembers in somewhat disturbing detail," Dan Pfeiffer, senior advisor to Obama, told the New York Times.

"Basically nothing gets done that involves the president doing anything without Alyssa being a part of it," Pfeiffer said.

Mastromonaco, 38, will help Obama with a foundation launched by supporters in January that will plan the building of his presidential library, the Times article said.

Reuters reported in December that Mastromonaco was considering leaving, one of several departures of long-term aides that has included counselor Pete Rouse and economic advisor Gene Sperling.

(Reporting by Roberta Rampton; Editing by Lisa Shumaker)