Julián Álvarez has said he left Manchester City after only two seasons to join Atlético Madrid because he needed "a new challenge."
The Argentina international, who had a contract with City through June 2028, completed his move to Atlético earlier this week for £82 million ($104m).
"I felt that I needed a change in my career," Alvarez said during his unveiling on Friday.
"I needed to look for a new challenge and I believe that this club gives me the tools to give my best."
Alvarez scored 19 goals in 54 appearances for City last season but failed to dislodge Erling Haaland as the first-choice striker in the team.
"I've come here to help the team and to fight for every title," Alvarez said. "I'm very happy and motivated.
"I spoke to [Diego] Simeone and he said he wanted me to come here. He said that I was going to help the team and they would enhance my strengths and help me improve on my weaknesses. My aim is to show my best form, help the team win and take Atlético to the highest level."
The 24-year-old won six trophies, including two Premier League titles and one Champions League at City. During his time at the club, he starred in Argentina's World Cup triumph in 2022 and also lifted the Copa América earlier this summer.
"I learned a lot there [at City]," Alvarez said. "I'm grateful for the two years I've been there."
Following his two seasons with Pep Guardiola, the forward spoke of looking forward to working under Simeone.
"They [Guardiola and Simeone] are among the best coaches in the world," he said.
"I don't feel a superhero for winning the World Cup. I still have a lot to learn and improve.
"I am very happy to be working with Simeone for what he means to this club and for world football."
Atlético begin their LaLiga campaign on Aug. 19 away to Villarreal.