Years on Def Jam: 2005-Present
Signature Def Jam Song: "Umbrella" (2007)

One of Jay-Z's best moves to date: As Def Jam president, he and L.A. Reid signed this ridiculously sexy hitmaker who through careful development has gradually turned her into an uber-starlet part Madonna, part Marilyn. Her unending string of hits for the label places her high on this list with a bullet.