Struggling West Ham said they had appointed David Moyes as manager for the second time in a bid to safeguard their place in the Premier League.
Moyes, whose career has never recovered from a deeply unsuccessful spell as Manchester United boss in 2013-14, succeeds Manuel Pellegrini, who was sacked after a 2-1 defeat to Leicester on Saturday that left the Hammers just one point above the relegation zone.
The 56-year-old has been without a club since leaving West Ham after a six-month spell in the 2017-18 season.
Moyes guided West Ham to safety that season after Slaven Bilic was dismissed in early November and will be tasked with doing the same for a second time.
"It's fabulous to be back," said Moyes in a club statement on Sunday.
"I'm feeling very proud that I'm back here at West Ham. But I think more importantly I'll be looking to see what I can do and what I can make improvements to.
"I do believe that the squad of players I've got here is a better squad of players than when I took over before, so I am looking forward to working with them."
"We are delighted to welcome David back - he knows the club well and he built strong relationships during that time which will be crucial for the work that needs to be done going forward."