Kanye West is, obviously, one of the most influential artists of the past decade-plus. His first impact hit in the early 2000s, as his production sound joined likeminded artists like Bink! and Just Blaze in reintroducing a soul-sampling style that contrasted directly with the synthesizer aesthetic that rose with the success of artists like Cash Money and Swizz Beats.
His revolution was also ideological. He stressed relateability and an accessible, regular-guy middle-class sensibility in a time when hip-hop still reflected a streets-oriented consciousness. He single-handedly created a lane that enabled artists from J. Cole to Mac Miller to Chance to Drake to thrive today.
His second major aesthetic revolution came with 808s and Heartbreak. Although it certainly didn't invent autotune, for a certain audience, it legitimized it, adapting the form and helping to popularize what is now an everpresent sound in popular music.