The Rams, mired in another losing season, fired Coach Jeff Fisher on Monday with three games remaining in the season, the team announced.
"Making a decision such as this — especially during the season — is one of the most difficult in sports," Rams owner Stan Kroenke said in a statement. "I have great respect for Jeff as a coach, person, father and friend.
"He has worked tirelessly despite some challenging circumstances. He played an integral role in helping this team make history in returning the NFL to Los Angeles, and we always will be grateful for his commitment and dedication to our organization.
"However, this is the right time to make a change as our performance has not lived up to my or our fans' expectations. We all are focused on improving as an organization and building a team that makes Los Angeles proud. Our mission is to celebrate a Super Bowl title with our fans in Los Angeles. Today is the first step to bringing us closer to that goal."
Special teams coach John Fassel was named interim head coach.
Kevin Demoff, the Rams' chief operating officer and vice president for football operations, said the decision to fire Fisher was "solely a performance-related issue."
Demoff, during a 40-minute news conference at the team's training facility in Thousand Oaks, described the situation as an "organizational failure" and said the move was "more about direction and hope."
The Rams' performance the last few weeks, "that really changed the barometer," Demoff said.
He said he spoke at length with Kroenke on Sunday night and then revisited the discussion Monday morning before informing Fisher.
"I don't think he was certainly expecting it," Demoff said of Fisher's reaction, which he described as professional.
Fisher spoke to assistant coaches and players before Demoff addressed the team and later organizational staffers.
Demoff said the Rams would consider candidates from all ranges of experience. He said "this is going to be a very attractive opening."
"The biggest mistake we can make is narrowing our search before it begins," he said.
The future of General Manager Les Snead will be determined at the end of the season as the Rams evaluate all parts of their operation.
Fisher was fired the day after the Rams suffered an embarrassing 42-14 loss to the Atlanta Falcons. After the game, running back Todd Gurley said the Rams had run "a middle-school offense" and said some players were not giving full effort.
The Rams are 4-9 and have lost eight of their last nine games. They play at Seattle on Thursday night.
Fisher, 58, was in the fifth and final year of a contract that paid him about $7 million a year. He received a two-year contract extension before or early in the season and is expected to receive a buyout.
Fisher and Snead were hired by the St. Louis Rams before the 2012 season. The Rams went 7-8-1, 7-9, 6-10 and 7-9 in the four seasons preceding the Rams' move back to Southern California.
Fisher coached the Houston Oilers in the mid-1990s and helped move the franchise to Tennessee, where it became the Tennessee Titans.
Fisher has a career record of 173-165-1. He is tied with Dan Reeves for the most losses by a coach in NFL history.
The Rams traded six draft picks to move up 14 spots and select quarterback Jared Goff with the top pick in the NFL draft.
But Fisher played journeyman Case Keenum and the Rams got off to a 3-1 start before spiraling to 4-9.
Fisher also has been embroiled in controversy with Hall of Famer Eric Dickerson, who has been openly critical of the team. Fisher and Snead also spent last week disputing a report that said their relationship was toxic.
4:04 p.m.: This article has been updated with comments from Rams COO Kevin Demoff.
12:00 p.m.: This article has been updated throughout with additional details and background.