One mark of an important artist is a spirit of rebellion, and rebellion is one thing that marked the work of Maurice Sendak. The children’s book author and illustrator, who died Tuesday at 83, made a mark on the literary world by refusing to pander to cautious parents or sugarcoat stories for young readers. Productive things can come of making people uncomfortable, which is what happened when the Beastie Boys descended, loudly and brashly, onto the music scene in the 1980s,. Co-founder Adam Yauch, who died of cancer last week at 47, played a key role in bridging the gap between urban hip-hop and disaffected white suburbia.