Mike Dean is the dude who adds all the dope bridges and little instruments on Kanye's tracks.
Recently he did work on Magna Carta Holy Grail w/ Somewhere in America & Crown. He did the outro to those two songs, which are without a doubt two of the best moments on the album.
Without Mike Dean, Kanye's beats right now wouldn't be shyt. He is responsible for the subtleties and dope harmonies and melodies Kanye has in most of his songs.
He also mixes and masters a lot of Kanye's shyt as well.
Dating back though, he worked with a lot of southern rappers (Geto Boys, UGK, Z-Ro, Devin the Dude, etc.)
Look him up on Wikipedia for his producer credits