Lopez, a four-time world champion, had been the clear favourite to retain the 120kg gold he won in Beijing four years ago.
Cuban supporters cheered wildly as Lopez did a lap of honour of the packed arena with his country's flag draped over his shoulders.
He beat Turkey's Riza Kayaalp in the semi-finals, settling a score with the young wrestler who defeated him in the world championships last year.
Lopez carried his country's flag at the opening ceremony of the London Games.
