MOSCOW--Russian economist Yegor Gaidar, mastermind of the controversial "shock therapy" economic reforms implemented under former president Boris Yeltsin, died Wednesday aged 53, his spokesman told AFP.

Gaidar died at 3:00 am (midnight GMT) while at work on a book, spokesman Valery Natarov told AFP, giving the cause of death as complications arising from a blood clot.

Gaidar, who also briefly served as Russian prime minister in the early 1990s, was the architect of the economic reform aimed at rapidly transforming Russia into a market economy after the collapse of the Soviet Union.

The reform was known as "shock therapy" after Gaidar decided to implement the massive changes within a very short period of time rather than progressively.