Argentina forward Taty Castellanos has joined West Ham from Lazio on a four-and-a-half-year contract with the option to extend for another year.
The 27-year-old, who scored 10 goals in Serie A last season, has signed in time to be available for Tuesday's Premier League clash with Nottingham Forest, West Ham said in a statement.
"I'm really happy because it's a very important challenge for me personally and I've come to contribute, to try to help the team as much as I can," said Castellanos, who will wear the number 11.
Hammers coach Nuno Espirito Santo had identified the former Girona and New York City FC player as a key target.
Relegation-threatened West Ham, who are winless in their last nine matches, are 18th in the table, four points below 17th-placed Forest.
"Every match is a battle. I'm going to give everything, to defend this jersey, and obviously, to achieve our goals day after day," Castellanos added.
