West Ham signed Ghana midfielder Mohammed Kudus from Ajax in a deal worth a reported £38 million ($47 million) on Sunday.
Kudus agreed a five-year contract with the Premier League club and becomes their fourth major signing since the end of last season.
The 23-year-old scored 19 goals and laid on seven assists in all competitions for Ajax last season.
He scored a hat-trick in Ajax's Europa League play-off win over Ludogorets in Bulgaria on Thursday.
"I've been dreaming to play in a league like this since I was a kid," Kudus told West Ham's website.
"I've been dreaming of this moment and I'm so happy to be here. But it doesn't stop here, I want to keep going.
"I try my best to entertain the fans as I think that's what football is all about. I can't wait to get started."
Kudus has won 24 caps for Ghana and featured in last year's World Cup in Qatar.
He had played for Ajax since 2020 and won two Dutch titles with the club.
West Ham had already signed Kudus's Ajax team-mate Edson Alvarez earlier in the summer.
England midfielder James Ward-Prowse and Greece defender Konstantinos Mavropanos have also arrived at the London Stadium as the Hammers spend the cash earned from Declan Rice's £105 million sale to Arsenal.
"I'm delighted we've been able to bring Mohammed to West Ham," Hammers boss David Moyes said.
"He's a terrific young talent, who has already shone at the very highest level for Ajax in the Champions League and made well over 150 senior appearances at the age of 23.
"It was no surprise to see so many top clubs chasing his signature this summer."