Once a skill reaches 100, you can make it legendary. The skill is reset to 15, and all perks are converted to perk points. Making a skill legendary allows you to level your character almost indefinitely.Once a skill has reached a value of 100, you have the option to make it Legendary on the Perk screen. This option resets the skill to a value of 15, and clears all its perks. You get back the perk points for all the perks that have been cleared.