Why is he important? He believed in an absolute right or wrong. He created the Socratic way of thinking. He taught Pluto, who taught Aristotle, who taught Alexander the Great.(1)
Why did he get sentenced to death? Athenian leaders believed that he taught his students to rebel against Athens during the Peloponnesian War, and that was the reason they lost.(1)
Why did he get sentenced to death? He was accused of corrupting the youth, but all he really did was embarrass and irritate the important leaders of Athens.(2)