He's the son of Odinn and Frigg, and brother to Bragi, Heimdallr, and Thor, among others.
Consorts & Children:
His wife is a goddess named Nanna, and it's through her that he sired Forseti, the god of justice.
Notable Stories Involving Him:
He was much beloved by gods and humans alike. Still, he started having dreams of his own death, dreams that were considered to be prophetic. So, his mother Frigg went around making everything in the world vow not to harm him, though neglected to extract the same vow from mistletoe, as she deemed it too insignificant. Loki, the only one of the gods who seemed to take issue with Baldr, learned of this, and tricked Baldr's blind brother Hodr into killing him with an arrow made of mistletoe. Odinn then sent his son Hermod to ask Hel, the goddess of death, to resurrect Baldr, and she agreed, on the condition that everyone in the world had to weep for him. Unfortunately, all but Loki wept, and so Baldr remained in the underworld. However, it's said that once Ragnarok, the end of the world, arrives, Baldr will be resurrected in the new world.
SOURCES: Wikipedia, Encyclopedia Mythica, & The Ultimate Online Resource for Norse Mythology and Religion