David Wagner has left his role as Huddersfield manager by mutual consent with the club bottom of the league.
The German, 47, took over as Terriers boss in November 2015 and led them to promotion to the Premier League in 2017 via the Championship play-offs.
Huddersfield were one of the favourites for relegation last season but Wagner guided them to a 16th-place finish.
However, they have struggled this term and are eight points from safety after taking 11 points from 22 games.
Wagner's departure a 'truly joint decision'
Town chairman Dean Hoyle called it a "sad day", adding that Wagner's achievements over the past three and a half years had surpassed his "wildest expectations" and make him one of the greats of the club.
Hoyle said: "We took this club to the highest position it has held in almost 50 years and created memories that will last forever.
"His achievements will rightly put him up there in Huddersfield Town history alongside great names like Herbert Chapman and Mick Buxton; legendary managers who changed the face of this club.
"As I have said previously, I had no intention of sacking David this season. Subsequently, David - being the great man he is - came to us and made it clear that he needs a break from the rigours of football management.
"We discussed making that change immediately, but he also made it clear he would give his all for the rest of this season before departing in the summer if we preferred.
"We all felt that David staying at the club until the end of the season was best, but we've kept discussions open and we all now feel that the time is right to part ways.
"I know the term 'mutual consent' is often a byword for the manager being sacked in professional football, but this is a truly joint decision. David has a real, genuine love for this club and, like me, his foremost concern in our talks has been to establish what is best for Huddersfield Town."
Wagner's last game in charge was Saturday's goalless draw at fellow relegation candidates Cardiff, when the visitors were denied a late penalty.
He was named Championship manager of the year after leading the west Yorkshire side into the top flight and claimed the Premier League manager of the month award in August 2017.
In all, Wagner had a 33.1% win ratio from his 154 games as boss.
Coach Mark Hudson will take charge of the next league game against champions Manchester City on Sunday.
Analysis - Wagner will be remembered with great affection
BBC Sport chief football writer Phil McNulty
There was genuine warmth tinged with sadness in the words of Huddersfield Town chairman Dean Hoyle.
And this was perfectly understandable given the scale of the charismatic German's achievements at the Terriers since he was a surprise appointment to replace Chris Powell in November 2015.
Wagner set aside the comparisons with his great friend Jurgen Klopp at Liverpool to fashion a side in his own image, full of energy, endeavour and fearlessness. They achieved what many had regarded as impossible when they reached the Premier League by winning a Wembley penalty shootout against Reading in May 2017.
If this was not enough, he produced another outstanding feat of management to keep the club in the Premier League last term. They showed grit and resilience against sides with much richer resources to stay up, safety assured with outstanding draws at newly crowned champions Manchester City and Chelsea at the campaign's climax.
Life has been tougher this season, though. Wagner's side have been undermined by a lack of a goalscorer and have won only twice. Relegation looks inevitable.
However, whatever the outcome this term, Wagner will be remembered with great affection as the man who brought the fairytale to Huddersfield and whose effervescent personality galvanised the club and the town during his time in west Yorkshire.