After clocking three minutes 34.18seconds, he said: "Four years ago I cried tears of sadness, now there are tears of joy.
"There have been many difficult moments in my career. It has been a tough year after working hard for eight years. In June I had respiratory problems and I didn't even know if I was going to go to the Olympics.
"I feel I deserve this because of the difficult moments from Atlanta until now.
"In the last 100m I had images of what happened in Sydney in my mind. But this time I felt I could win."