Leonidas was the youngest of three children: Dorieus, Cleomenes (or Kleomenes) and Leonidas, so he was never expected to rise to the throne, therefore he took part in the agoge,
the unique training of Sparta usually spared from the royal heirs. Dorieus was born after Cleomenes but was fully legitimate, Cleomenes dealt with him and gained the throne. He ruled successfully for many years before going mad and mutilating himself to death. Thus Leonidas beacame king much to his suprise. He didn't last long. With the impending attack of Xerxes force on the peloponese, Leonidas consulted the oracle and got the answer: 'either a king dies at the walls of Thermoplyae or Sparta falls' a no-brainer really. Leonidas couldn't take all his army as the ephors refused to allow him to interrupt Carniea, a festival to Apollo. Leonidas held out for three days at thrmopylae with 300 Spartans and a collection of men from thespia, Athens, thebes and however felt like helping numbering about 7000 in all. In the morning of the second day, Leonidas sent all but the Thebans home, but the Thespians stayed. He told them (as features in the feature film) to 'eat a full and hearty breakfast, for tonight we dine in Hades'.