Fingolfin was the second son of Finwë and brother to Fëanor and Finarfin. He was rather more level-headed than his older brother and often advised his father to think twice before acting on Fëanor's advice. This eventually angered Fëanor to the point where he threatened Fingolfin with a sword in public, thus causing the older brother's exile.
During that time, Fingolfin ruled in place of his father. Eventually, however, he was reconciled with Fëanor and promised to follow his lead. This promise led to his involvement in the first Kinslaying, and his exile from Valinor.
After Fëanor's death, his son Maedhros chose to refuse the title of High King of the Noldor and passed it to Fingolfin, who kept it until his death in the Dagor Bragollach.
He was eventually killed in battle with Morgoth in front of the gates of Thangorodrim, Morgoth's fortress, but not before he had given the former Vala several fairly substantial injuries (such as cutting off his foot).
Fingolfin was the father of three children (four in later writings): Fingon, who succeeded his father as High King of the Noldor; Turgon, who later became the king of Gondolin; and Aredhel Ar-Feiniel, the White Lady of the Noldor. A third brother, Argon, was killed in an early battle with Orcs and didn't make the cut of the published Silm.