Original: According to Plato's Apology, Socrates' life as the "gadfly" of Athens began when his friend Chaerephon asked the oracle at Delphi if anyone was wiser than Socrates; the Oracle responded that none was wiser.
Simplified: It is said that one of Socrates' friends asked an oracle (a holy person that was wise, respected and who people thought could talk to the gods), if there was any person wiser than Socrates in Athens. The oracle said that there was no wiser person.