Luis Diaz will wear the No 23 shirt at Liverpool after his £50m move was completed.
The Colombian heads to Anfield from Porto after the Reds fought off competition from Premier League rivals Tottenham.
Diaz will compete with Sadio Mane and Mo Salah for a starting berth.
His new shirt number has previously been worn by the likes of Jamie Carragher, Emre Can, Xherdan Shaqiri and Robbie Fowler.
Diaz's move is set to cost an initial £37.5m, with £12.5m in additional payments based on performance.
Reds boss Jurgen Klopp is a huge fan of the Colombian, who was the joint-top scorer at last year's Copa America and has struck 14 goals in 18 Portuguese Primeira Liga matches this season.
Have Your Say! Will Sadio Mane remain first choice at Liverpool with Luis Diaz arriving? Tell us here.
He told the club's website on the signing: “I could not be happier that we’ve been able to get this deal done and bring Luis to Liverpool.
“I have always been a believer in only signing players in January if you would want to sign them in the summer, and that’s very much the case with Luis.
“He is an outstanding player and someone we’ve been tracking for a very long time.
“We believe he has everything needed to fit into our way and adapt to the Premier League, both physically and mentally. He is a player who is hungry for success and knows you have to fight to get what you want.
"He is a fighter, no doubt. He’s a skilful team player who has always the goal in mind.
“This team deserved to add quality and when we played against Luis earlier this season, we saw what a danger he is, how fast he is and how his mentality was to help his team."
Diaz will join up with the Liverpool squad once he has finished his international duties. The club stated on their website that Diaz has signed a long-term deal.
The move is subject to the successful granting of a work permit and international clearance.
Liverpool have previously exercised the January market effectively with the likes of Philippe Coutinho and Virgil van Dijk both arriving midseason.
Diaz will bolster a forward line that already includes Mane, Salah, Diogo Jota and Roberto Firmino.
The Reds are still fighting on all four fronts this term and will need to exercise their squad depth.
A Carabao Cup final against Chelsea is to come next month whilst they remain in the FA Cup and the last 16 of the Champions League.
In the Premier League Klopp's side were able to cut the gap to Manchester City last weekend and Diaz will provide a fresh injection ahead of the business end of the campaign.
