This is taken from the Verge's article
As part of the agreement, Nokia CEO Stephen Elop is stepping aside; he's now leading Microsoft's Devices team. That puts him in an odd position with Julie Larson-Green, who Ballmer said will be joining his team, but will also be responsible for other hardware like Surface and the Xbox One. The exact scope of Elop's role isn't exactly clear, and with a soon-to-be-vacant CEO seat we expect plenty of rumors to fly as the acquisition closes. Risto Siilasmaa was named Nokia's Interim CEO — he was previously chairman of the company's Board of Directors.