Def Jam founded by Russell Simmons, Rick Rubin & DJ Jazzy Jay (Jazzy Jay introduced between them) and is the most important hip hop music label in history (Although it isn't 100% hip hop).

Also check Def Comedy Jam (<<< Click)

The first single out on Def Jam in 1983 - T-La Rock & Jazzy Jay - It's Yours:

The first "12 single with catalog number was LL COOL J - I Need a Beat:

Ski talks about Def Jam (Jay-Z, Pittsburgh Slim)

Jay-Z Def Jam's videos

Rihanna's video from Def Jam - Signed by Jay-Z

LL Cool J - I Need Love Video