Timeanddate.com wrote:Leif Erikson Day honors a viking explorer known as Leif Erikson. He is believed to be the first recorded Nordic person to have visited North America. It is believed that he visited places such as Baffin Island and Labrador around 1000 CE.
Here's a relevant clip from the SpongeBob SquarePants episode Bubble Buddy, where most people have heard of Leif Erikson Day in the first place. It's not a made up holiday contrary to what the narrator said from the start of that very episode, but it isn't a federal holiday either sadly.