https://www.gamespot.com/articles/fortnite-founders-pack-skins-see-the-two-exclusive/1100-6460688/

Epic Games is currently celebrating Fortnite's 1st birthday with new challenges that will unlock emotes, sprays, and bling. However, it's also offering some extra skins to those that have been with the game from the very start. Fortnite originally launched with just the mode that is now known as Save the World, and was available to purchase as a Founder's Pack. When the Battle Royale mode was later launched, those that had purchased the Founder's Pack were promised some free skins, and almost a year later they've materialised.