Shamrock Shakes are a green, minty treat from McDonald’s available in most of March in honor of St. Patrick’s Day. You might not know this, but Shamrock Shakes have an important history. For starters, they were one of the first big seasonal drinks at the national food chains. But, more importantly than that, Shamrock Shakes had a lot to do with the founding of the Ronald McDonald House.

Although Connecticut franchisee Harold Rosen claims to have invented the shake in 1966, McDonald’s official corporate history says the drink was invented in 1970. One way or the other, Shamrock Shakes didn’t become a big thing until 1975. That’s when the daughter of Fred Hill, a tight end for the Philadelphia Eagles football team, was diagnosed with leukemia.

Fred ended up spending a lot of time in hospital waiting rooms, and he noticed several other families doing the same. These folks had traveled long distances to get treatment for their children, but it bothered Fred that costly medical bills prevented mothers and fathers from getting hotel rooms during their stays. It just didn’t seem right to Hill that parents had to camp out for days at a time in waiting rooms, so he asked his teammates to help him raise funds to buy a house for the parents.

When Jim Murray, the Eagles’ general manager, heard about Hill’s cause, he called a friend who worked in McDonald’s PR department. Murray suggested that the fast food giant use the shake as a PR tool for Hill, as St. Patrick’s day was approaching and the shake was green, like the Eagles’ uniforms. Murray’s friend agreed, and by the end of the month enough cash had been raised to buy a four-story house, which became the first Ronald McDonald House. Since then, a portion of the Shamrock Shake sales has been donated to the Ronald McDonald House charity.

Enjoy this 80s-licious Shamrock Shake commercial:

I tried to find a commercial with Uncle O’Grimacey, Grimace’s Irish uncle, but the quality of the videos I found on YouTube was… lacking. So enjoy this picture instead: