Autosport's technical editor Jake Boxall-Legge runs through the reasons why Renault eventually landed on Alonso, and how the veteran Spanish driver can possibly breathe new life into a stagnating team.
Alonso stepped away from F1 at the end of 2018 following a hard four-year spell at McLaren without a victory or a podium. Alonso, who won back-to-back championships with the French team in 2005 and 2006, will celebrate his 39th birthday later this month.
The 39-year-old, who is a two-time Le Mans 24 Hours victor, won his championships in 2005 and 2006 and drove for McLaren in the 2018 season.
Renault needs a replacement for Australian driver Daniel Ricciardo, who will join McLaren at the end of this season. "This decision is both bold and meaningful for the future". His experience and determination will enable us to get the best out of each other to take the team towards the excellence that modern Formula One demands.
"It's a great source of pride and with an vast emotion I'm returning to the team that gave me my chance at the start of my career", Alonso said.
"Fernando joins Renault for the upcoming seasons", Renault said. While he was away, he won the Le Mans 24 Hours twice with Toyota.
Halo Infinite gameplay reveal likely part of Xbox Games Showcase
It forms the next in Microsoft's series of Xbox 20/20 events teasing the upcoming next-gen console and its accompanying games. Microsoft previously held a special Inside Xbox stream in May, but that was to showcase new third-party and indie titles.
"I have principles and ambitions in line with the team's project".
Team Principal Cyril Abiteboul said part of Alonso's role will be to offer and advise and support to young prospects coming through the Renault Sport Academy.
However, because of rule changes teams will use the same cars for 2021 and Alonso may not have a genuinely competitive auto until 2022, when he will turn 41 in late July.
He also narrowly missed out on another three World Championships - in 2007 with McLaren, and in 2010 and 2012 with Ferrari.
The two-time world champion last raced in a grand prix at the end of the 2018 season and left F1 saying he had nothing more to achieve in the series.
McLaren struggled badly after switching to a Honda engine, and he failed to secure a podium finish in four seasons.
With less preparation than ever for the Indy 500, Alonso described the outcome as being "a coin in the air".