In 1987, Cosmonaut Yuri Romanenko ended his record 326 day mission orbiting the Earth in the Mir space station.
Yuri Romanenko’s stay in space broke the previous Soviet record of 237 days and the U.S. space endurance record of 87 days. He held the record until 1995 when it was broken by Vladimir Titov and Musa Manarov with a stay of 366 days in space. Later that same year, the record was broken again by Valery Polyakov with 438 days in space.
Learn more at http://spaceflight.nasa.gov/history/shuttle-mir/spacecraft/s-mir-records-main.htm.