Fisher was let go with the Rams (4-9) mired in a four-game skid. He went 31-45-1 in his stint with the team, including four seasons prior to 2016 in St. Louis.
"First and foremost, I want to thank (owner) Stan Kroenke for the opportunity to be part of this organization the last four and a half years," Fisher said in a statement. "I want to thank the entire football staff as it has been a privilege to work with each one of them day in and day out.
"I especially want to thank all of the players. They are a great group of men that I respect, and that I will greatly miss. My hope is that each one of the players experience great success in the future."
One of the more interesting situations during Fisher's first season in Los Angeles was the grooming of No. 1 overall pick Jared Goff.
While many people were clamoring for the quarterback to take the field, Fisher decided he wouldn't start the rookie until he felt he was ready.
Goff finally became the starter in Week 11. And he was pretty disappointed to learn Fisher wouldn't be the team's coach in Week 15 against the Seattle Seahawks.
"He's a guy that, I think I speak for the whole team when I say, was very well liked, very giving, and he treated us the right way -- he treated us the way we're supposed to be treated," Goff told reporters.
"And in return we didn't do enough for him. That's really what it comes down to -- is we didn't get it done and unfortunately it falls on him. Us in the locker room blame ourselves and we need to be better."
The firing also came just eight days after Fisher's contract extension became public.
Special teams coordinator John Fassel is the interim head coach. He has been with the team for five years and is the son of Jim Fassel, a longtime NFL coach who guided the New York Giants to the Super Bowl during the 2000 season.
The timing of the dismissal saved Fisher -- at least temporarily -- from setting a dubious all-time NFL record. Fisher is 173-165-1 in his career and one more defeat would surpass Dan Reeves (165) for the most career losses by an NFL head coach.
With the Rams spiraling toward their fifth consecutive losing season under Fisher in their first year back in Los Angeles after a 21-year absence, the timing of Fisher's contract extension -- reportedly for two years -- was curious. However, the deal actually was agreed to in the preseason and signed during the season.
Kroenke found it painful to remove Fisher as coach.
"Making a decision such as this -- especially during the season -- is one of the most difficult in sports," 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."
In 22 seasons as an NFL head coach with the Tennessee Titans and Rams, Fisher led his teams to the playoffs just six times, including getting the Titans to the Super Bowl before losing to St. Louis in 2000.