Mikhail Kalashnikov, the 94-year-old inventor of the world’s most popular firearm, the AK-47, died Monday, Dec 23, in a Russian hospital, a local government official said, according to RIA Novosti.

“We received sad news today: legendary small-arms inventor Mikhail Kalashnikov died at the age of 94 after a prolonged illness,” Viktor Chulkov, a spokesman for the head of the Udmurtia republic, Kalashnikov’s home region, said in Facebook post.

Kalashikov had been recently admitted to an intensive care unit at a hospital in Udmurtia’s regional capital, Izhevsk, while “in serious but stable condition,” according to the local branch of Russia’s Health Ministry.

In June, the famed weapons designer underwent an operation in Moscow to have a pacemaker implanted.