Ruathars are those who have earned the special friendship of the elven folk. While many individuals have a good connection with the elves, the ruathar has mystically linked to the Fair Ones. The elves that see the ruathar for what he is, respect him and offer him assistance wherever he goes. Elves can become ruathar, but only if he helps elves not in his home region, or if he is a Forlorn who tries to redeem himself.
Ruathars have to be heroes so should have some ability, be it in combat, magic, or skill. In addition, he has to perform some important task for the elven community (such as risking his life in order to save an elf’s life). Ruathars gain proficiencies with elven weapons and ruathars with spellcasting ability gain magical power and every ruathar learns a small magical phrase that identifies himself as a friend of the elves. Ruathar also gain elven traits, such as slightly larger pupils (granting low-light vision and the elven perception bonus). More so, the night sky seems to smile upon the ruathar, granting him better combat ability at night. At last, the love of the elven folk actually changes the ruathar, granting him a longer life and gives him the ability to take on other career paths only elves could take.
Sources: Races of the Wild