The Williams Formula 1 team's chief technical officer Pat Symonds will leave the team at the end of this year.
Symonds, 63, has been Williams's technical boss since joining the team from Virgin Racing - now Manor F1 - in mid-2013, with Williams saying he signed a three-year contract when he arrived.
In his first full season after joining, 2014, Williams finished third in the constructors' championship, a feat it repeated in 2015. But this year the team slipped to fifth in the table, behind fellow independent Force India.
Symonds' departure comes amid strong rumours that Paddy Lowe, executive director (technical) of Mercedes, is due to switch to Williams, in a senior technical role.
In a statement confirming the move, deputy team principal Claire Williams said: "Pat has been a tremendous asset to this team over the past three years.
"Pat's appointment was the start of a major restructuring exercise, and he has been pivotal in reshaping Williams into what is a much stronger racing team today.
"I would like to thank him for all of his hard work and commitment during that time.
"We now look to the future and will be announcing details regarding the team's technical leadership in due course."
Symonds, an aerodynamicist by training, has been a leading F1 engineer since the early 1980s, when he joined the Toleman team.
He remained with the team when it was taken over by Benetton in 1984, staying on again when it became a Renault 'works' entry for 2002.
As executive director of engineering, Symonds remained a central figure at the Enstone-based squad when its success peaked with back-to-back drivers' and constructors' titles with Fernando Alonso in 2005 and '06.
He had previously worked with F1 champions Ayrton Senna, Michael Schumacher and Nelson Piquet, as well as numerous race winners including Giancarlo Fisichella, Jarno Trulli and Gerhard Berger.
Symonds' Renault career was marred by his involvement in the 2008 Singapore GP crash scandal, for which he was suspended from F1.
This ban was later overturned, with Symonds receiving compensation and permission from the FIA to return to a full-time role in the sport.