The shakes were first launched in the U.S. in 1970 and were initially called the "St. Patrick’s Day Green Milkshake" before adopting the name "Shamrock Shake".
Harold Rosen, a McDonald's franchisee owner in Enfield, Connecticut, claimed to have invented the shake in 1966. The McDonald’s Corporation has disputed Rosen's claim.
In 1978, McDonald’s introduced Uncle O’Grimacey (the Irish uncle of Grimace) as way to promote the shakes. The character was phased out in the early ‘80s.
McDonald's introduced the Shamrock Sundae in 1980.
But, due to poor sales, the sundae was discontinued after one year.
The Shamrock Shake and the Philadelphia Eagles led the creation of the Ronald McDonald House.
Shamrock Shakes were discontinued nationally in the early ‘90s. Its cult following and huge Internet presence led to it being re-introduced in the late-‘00s.