Socrates is acknowledged as the father of Western philosophy, a great teacher who taught Plato, who in his turn taught Aristotle, Alexander the Great's teacher. Beyond philosophy, Socrates was a brave and skilled soldier who once saved the life of Athenian general Alcibiades.
Socrates' primary interest was in using philosophy as a tool to make society better. In service to that goal, he taught a system of rational ethics to the young men (and future leaders) of Athens, using the Socratic Method, a system of questioning to reach an answer, to ensure they learned to think for themselves. This technique did help people come to rational conclusions, but because it also revealed how foolish didactic beliefs were, it made many enemies as well.
Socrates' insistence upon people facing the truth ultimately led to his downfall. During his lifetime, Athens was in social turmoil. The city-state had lost to Sparta in the Peloponnesian War and was having a collective crisis, turning to past glory and beauties instead of facing the tough future. When Socrates challenged this and taught his young students to challenge it, he was charged with corrupting Athenian youth. After a trial, he was sentenced to death. Though his followers were willing and able to smuggle him out of the city into exile, Socrates willingly drank the hemlock that killed him.