The 27-year-old pens a three-year contract after the Latics agreed an undisclosed fee with the Spanish side, who were relegated from La Liga last season.
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"I think our fans will like him; he is very direct and physical, good in the air, a real worker, but also has an eye for goal, scoring the majority of his goals inside the box," Rosler told Wigan's official website.
"He has attracted the attention of many clubs and we are delighted he has agreed to join us.
"He is in the prime of his career and is physically and mentally ready to take the challenge of coming to England. He is definitely the type of player we have been missing in our squad."
Riera - who scored 13 goals in 37 league appearances last term - is thrilled to have completed his switch to England and revealed that former Wigan star Jordi Gomez played a part in his decision.
"I am really pleased to become a Wigan player," he declared. "My friend, Jordi Gomez, spoke really highly of everyone here and that makes me excited to get started."