The 44-year-old marksman had shot his way to two bronze medals during his previous five Games appearances, but this time he utterly outclassed his rivals at the Woolwich venue.
After scoring a perfect 600 in qualifying, he began the eight-man final strongly, extending his lead to 3.2 after six rounds.
With near-faultless precision and nerves of steel he shot a maximum 10.9 in the ninth round to bring the crowd to its feet. Going into the final round he had built up a 4.1 lead and eventually set a new world record of 705.5.
Dubbed ‘The Man Who Does Not Smile’, the new champion allowed himself a small grin and punched the air. And he couldn’t hide his pleasure on the medal podium as he was presented with the gold medal.
He said: ‘I am absolutely delighted. This will mean everything to my country. I have been over 15 years in this discipline and it is one of the best feelings.’
Martynov first competed in the Olympic Games in the 10m air rifle event in Seoul in 1988 and has taken part in every 50m rifle prone competition since the Atlanta Games in 1996.
Since 1997 he has shot a perfect 600 six times – more than any other rifleman. But after winning bronze in Sydney in 2000 and again four years later in Athens, and then being crowned world champion in 2066, he suffered a dip in form in Beijing and finished in eighth place.
After his London victory in the contest – where competitors fire at a 10-ring stationary target from a lying position – he revealed that he shot his way to victory using a 13-year-old gun and bullets from the Soviet era, the same equipment that brought him his previous two Olympic medals.
He told reporters: ‘A rifle isn’t a wife but you have to look after it and give it tender, loving care. I’m not prejudiced against any recently made rifles or rounds – it is just when you choose a gun you choose something that feels more comfortable.