We know that James and John ("the beloved disciple") were brothers. We know that Peter, James, and John were extremely close to Jesus, going places with him that the others did not go - especially his moments of glory on Mt. Tabor and agony on the Mt. of Olives - their moments of shame.
We can infer that he (and therefore John) may have even been humanly related to Jesus which could also explain their closeness. We know so much about James that we do not know about other Apostles except through Tradition.
James and John, as siblings and possible relations, seem to also take some liberties not available to the other apostles, perhaps relying on that unique closeness to Jesus.
We really know James from these great yet intimate moments provided to us from Scripture. We see his humanity and his wisdom; we see him in vanity and selflessness. I only hope, for myself in vanity and pride, that if ever anyone portrays me, that they leave out such intimate details, that I remain in the background like some of the more anonymous apostles and disciples.
After the death and resurrection of Jesus, Scripture tells us even more about James; we know him as leader of the Church in Jerusalem, as a leader at the Council of Jerusalem, and as the first apostle to be martyred.
We get to see James before the Resurrection and after the Resurrection. We are able to see the transition from follower to leader; we see the confidence placed in his wisdom to lead the foundation and home base of the Church. In the first challenge to the Church he stepped forward and helped to clarify and support the changes to the early theology that we depend on so much today.
What becomes important when theology changes? Adherence to the Truth, the Truth not as we understand it, but as the Apostles handed on to us - the words, thoughts, and meaning of Jesus.
So it is not us who decide. In the end none of our speculation matters. As John Chrysostom points out below, our human thinking is flawed in the face of God, and God will always show us the truth, and that truth is for God's glory not our own.
James helped to guarantee that the glory and praise belong to God alone.
James, pray for our leaders and teachers.
So far at least were they from understanding clearly what He said, that the sons of Zebedee at the same time came to Him, and spoke to Him of precedence. "We desire," it is said, "that one should sit on Your right hand, and one on Your left." ...But rather let us learn, first, what do they ask, and with what disposition, and whence they were moved to this? Whence then were they moved to this? They saw themselves honored above the rest, and expected from that they should obtain this request also. ...Wherefore also Christ in the first place leads them off from these thoughts, commanding them to await slaughter and dangers, and the utmost terrors. For, "Are you able," says He, "to drink of the cup that I drink of?" But let no man be troubled at the apostles being in such an imperfect state. For not yet was the cross accomplished, not yet the grace of the Spirit given. But if you would learn their virtue, notice them after these things, and you will see them superior to every passion. For with this object He reveals their deficiencies, that after these things you might know what manner of men they became by grace. That then they were asking, in fact, for nothing spiritual, neither had a thought of the kingdom above, is manifest from hence. But let us see also, how they come unto Him, and what they say. "We would," it is said, "that whatsoever we shall desire of You, You should do it for us." ...But they out of shame and confusion of face, because under the influence of a human passion they had come to do this, took Him privately apart from the disciples, and asked Him. For they went before, it is said, so that it might not be observable to them, and so said what they wished. For it was their desire, as I suppose, because they heard, "You shall sit on twelve thrones," to have the first place of these seats. And that they had an advantage over the others, they knew, but they were afraid of Peter, and say, "Command, that one sit on Your right hand, one on Your left;" and they urge Him, saying, "Command." What then says He? Showing, that they asked nothing spiritual, neither, if they had known again what they were asking, would they have ventured to ask for so much, He says, "You know not what ye ask," how great, how marvelous, how surpassing even the powers above. After that He adds, "Are you able to drink of the cup that I shall drink of, and to be baptized with the baptism that I am baptized with?" Do you see, how He straightway drew them off from their suspicion, by framing His discourse from the contrary topics? For you, He says, talk to me of honor and crowns, but I to you of conflicts and labors. For this is not the season for rewards, neither shall that glory of mine appear now, but the present time is one of slaughter, and wars, and dangers.
And see how by the form of His question, He both urges and attracts them. For He said not, "Are you able to be slain?" "Are you able to pour forth your blood?" but how? "Are you able to drink of the cup?" Then to attract them to it, He says, "Which I shall drink of," that by their fellowship with Him in it they might be made more ready.
And a baptism again calls He it; showing that great was the cleansing the world was to have from the things that were being done.
-- John Chrysostom, Homily 65 on Matthew