This James is referred to as "the Lord’s brother" in Matt. 13:55, Mark 6:3, Gal. 1:19, called simply "James" in Acts 12:17, 15:13, 21:18, and 1 Cor. 15:7, and is considered by most scholars to be the author of the New Testament Epistle of James.
In A.D. 62, James the brother of Jesus and leader of the Jerusalem community was executed. This was a great blow, for James was a deeply dedicated figure whose obvious piety and prudent leadership had commended the new faith to many over more than two decades. His most striking testimony had been that commitment to Jesus in no way required severance from Jewish roots. The consistent Jewishness of James' theology is evident in the Epistle of James that exists in our New Testament. (Davidson, The Birth of the Church, p. 131)
Josephus concerning James
"Festus was now dead, and Albinus was but upon the road; so he assembled the sanhedrin of judges, and brought before them the brother of Jesus, who was called Christ, whose name was James, and some others, [or, some of his companions]; and when he had formed an accusation against them as breakers of the law, he delivered them to be stoned" 
- Ivor J. Davidson, The Birth of the Church: from Jesus to Constantine, AD 30 - 312, in The Baker History of the Church, vol. 1. (ISBN 0801012708)