James the Greater is one of the twelve apostles; he is brother to John and a son of Zebedee. He is the James of the “inner circle” of “Peter, James, and John” who was present at the Transfiguration. He was martyred in the early 40s AD.
James the Lesser is a moniker for James son of Alphaeus; he is the second of the twelve apostles known as James. If he is not the same man as “James, the brother of the Lord,” then this is likely just about all that is known of him.
James, the brother of the Lord, is just that, a close relative of Jesus–probably a step-brother born of Joseph’s previous wife, or perhaps a cousin of Christ. He became the Bishop of Jerusalem and was a prominent figure in the early Church.
I am of the opinion that James the Lesser and James, the brother of the Lord, are the same man. That there appears to be only one James of any significance following the martyrdom of James the Greater is a fairly strong indicator that the two appellations refer to one person. Furthermore, that the early Church did not distinguish between the two and that there are not separate stories regarding their lives or deaths post-Ascension gives me some confidence in this view.
Some would argue that James’ being named among Jesus’ “brothers” in Mt and Mk constitutes an indication that James son of Alphaeus is another person. That, however, is a specious argument. First, because the men listed could have been cousins to Jesus, which would allow for James’ father to be Alphaeus rather than Joseph; second, because there is no reason to believe that those in the crowd would refrain from naming one of Jesus’ “brothers” solely on account of his being a disciple.
The only other argument against the two being distinct figures is that it ought to be more obvious if the two monikers refer to a single person. Again, I believe that the fact that James, the brother of the Lord, need not distinguish himself from James, the second of the twelve, speaks to that point.