The Gospels are generally light on descriptions of the 12 apostles. Most of the apostles don't appear very often and typically when they do appear, it is only in name.
One interesting description that is given in the Gospel of Mark is when Jesus appears to using a nickname for the brothers, St. James and John.
Sons of thunder
The Gospel of Mark narrates the calling of the 12 apostles and adds the detail that Jesus called the brothers "sons of thunder":
And he went up into the hills, and called to him those whom he desired; and they came to him. And he appointed twelve, to be with him, and to be sent out to preach and have authority to cast out demons: Simon whom he surnamed Peter; James the son of Zeb′edee and John the brother of James, whom he surnamed Bo-aner′ges, that is, sons of thunder; Andrew, and Philip, and Bartholomew, and Matthew, and Thomas, and James the son of Alphaeus, and Thaddaeus, and Simon the Cananaean, and Judas Iscariot, who betrayed him.
One possible explanation is given by the Catholic Encyclopedia, claiming that James and John had a fiery temper and were very zealous in their desire to evangelize:
Several incidents scattered through the Synoptics suggest that James and John had that particular character indicated by the name "Boanerges," sons of thunder, given to them by the Lord (Mark 3:17); they were burning and impetuous in their evangelical zeal and severe in temper. The two brothers showed their fiery temperament against "a certain man casting out devils" in the name of the Christ; John, answering, said: "We [James is probably meant] forbade him, because he followeth not with us" (Luke 9:49). When the Samaritans refused to receive Christ, James and John said: "Lord, wilt thou that we command fire to come down from heaven, and consume them?" (Luke 9:54; cf. 9:49).
The Encyclopedia of the Bible also mentions that "Jerome thought it referred to their fiery eloquence; others have taken it as referring to their fiery dispositions. It may be that they were at one time zealots or revolutionaries. Perhaps the epithet reflects the ancient mythology about the Dioscuri (Heavenly Twins), the Sons of Zeus or Thunder."
Scholars continue to debate the exact meaning of the phrase and what Jesus was referring to when he named James and John the "sons of thunder."
