Minnesota's longest-serving congressman, Jim Oberstar, passed away early on Saturday in his sleep at the age of 79.

No cause of death was announced, but his former chief of staff, Bill Richard, said that the veteran Democrat hadn't been sick, reports WCCO. He is survived by his wife, four children and eight grandchildren.

Oberstar served as a Minnesota representative for 18 terms, from 1975 to 2011, when he was defeated by Chip Cravaack. The Eighth Congressional District is now held by Congressman Rick Nolan, according to the Star Tribune.

The former congressman's aide Ken Hasskamp said, "I'm just shocked. History will record him as the quintessential congressman -- the complete package."

According to Politico, Oberstar served on the Transportation and Infrastructure Committee as chair while in office.

After he was defeated in the 2010 election, which saw many Republicans snag seats away from Democratic congressman, Oberstar seemed happy with what he had accomplished in office, pointing out the Duluth lakewalk, new airport terminal, bike and hiking trails and the building over Interstate 35 overpasses.