Taken from "Spruce Eats":"The Harvey Wallbanger is a fun and simple vodka cocktail that was created in the 1950s. The recipe is very simple: mix a screwdriver and top it with a Galliano float. Galliano L'Autentico is a golden-colored sweet liqueur made with a blend of herbs, spices, and vanilla. A Harvey Wallbanger is a fruity, sweet, and herbal mixture that's totally refreshing.
As with many cocktails, there are a couple of claims to the creation of the Harvey Wallbanger. One is that it may have been created as an "all I got left in the bar" drinks. Supposedly, the host of a party in the mid-60s had only vodka, orange juice, and Galliano available. After a couple of these drinks, a guest named Harvey was found to be banging his head against the wall and cursing the drink that caused him his misery.
That's a fun story, but it's not very believable. The accepted truth attributes the Harvey Wallbanger's creation to Donato "Duke" Antone who owned Duke's Backwatch Bar in Hollywood. It was at this Sunset Boulevard joint in 1952 that Antone created the cocktail. He named it after a local surfer and bar regular named Tom Harvey.
It was not until the late 1960s that a marketing director for the company importing Galliano 'discovered' the drink. George Bednar created a surfer-themed ad campaign with the tagline "Harvey Wallbanger is the name, and I can be made!" By the time the disco era began, the drink was on everyone's lips. The 70s may have been the cocktail's glory days, but little gems like the Harvey Wallbanger are unforgettable."