Freyr is the god of fertility, virility, weddings, and wealth. He is the lord of Alfheim, which basically makes him the King of the elves.
He is the twin brother of Freyja. His father is Njörd, who conceived the twins with his sister (her name is unknown). He has produced a child with Gerd, a giantess that he had fallen in love with.
Freyr had a bunch of legendary artifacts that would help him during his adventures. He was accompanied by a golden boar, Gullinbursti, whose fur would shine so brightly that it would light his way when riding it through the sky. This animal was created for him by the dwarfs Brokk and Eitri, who created it with an old pigskin and dwarven magic. Another group of dwarfs, the sons of Ivaldi, made him the ship Skidbladnir, which was a ship that would always catch a favorable wind. Freyr could fold the ship so that it would fit in his pockets: a ship on the go. Last, but not least, he had a sword that would fight by itself, which practically made him invincible.
Freyr is destined to die at the hands of Surtr, the fire giant of Muspelheim. This will happen during Ragnarok. Things might have turned out differently if he would not have given his self-fighting sword away before the battle before he could marry Gerd, the giantess.