Lietaer joins the agency after a 10-year stint with JWT in Toronto, New York and London.
In London most recently, Lietaer was managing partner for JWT, where he formed a partnership with executive creative director of JWT London Nick Bell to win Allied Bakeries' pitch against DLKW, HHCL (now United London) and Publicis.
In addition, he led Smirnoff's development of a new campaign.
He was responsible for Diageo overall and also established a new relationship with MTV Europe Foundation.
At JWT New York, Lietaer was global account director on Diageo's Smirnoff portfolio -- Smirnoff, Smirnoff Ice and Smirnoff Twist.
Later, he managed a Cannes winning campaign for Kellogg's.
Lietaer said: "Wieden & Kennedy is an agency I've always admired. The depth and range of talent is amazing and the work they do for their clients is second to none.
"It wasn't exactly a tough decision -- Wieden & Kennedy and global Coca-Cola equals a no brainer. The team has been developing some great work. The most exciting is yet to come."
Tim O'Kennedy, managing director of Wieden & Kennedy, said: "Ryan comes to us with ringing endorsements from his former colleagues and clients.
"So we're very excited about Ryan and think he'll be a hugely positive addition to an already strong team.
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