Who is the brother to Jesus Christ?

Everyone who believes that he is the Christ and he died for our sins and was risen in three days and now sits at the right hand of God.


Other than that... Jesus had four step-brothers: James, Joses, Simon and Judas -(Matt.13:55). And at least two step-sisters (verse 56).

Here's a little more detail on this:
Mary and Joseph had no children before Jesus (Matthew 1:18-21, 24&25 ), but a number of scriptures mention "the Lord's brothers," "the brother of the Lord," "his brothers," "his sisters," naming four of the "brothers": James, Joseph, Simon, and Judas. (Matthew 12:46; 13:55, 56; Mark 3:31; Luke 8:19; John 2:12; Acts 1:14; 1Corinthians 9:5).
During Jesus' ministry, "his brothers were, in fact, not exercising faith in him," this would certainly rule out their being his brothers in a spiritual sense. (John 7:3-5) Jesus contrasted these fleshly brothers with his disciples, who believed in him and who were his spiritual brothers. (Matthew 12:46-50; Mark 3:31-35; Luke 8:19-21).
Jesus had at least four brothers and two sisters that were offspring of Joseph and Mary by natural means after the miraculous birth of Jesus.(Mark 6:3)
Jesus' brother James, who was singled out prominently among the older men in Jerusalem, wrote the letter bearing his name. (Ga 1:19)

In addition to the above, the brother of Jesus, James, is also singled out a great deal in Acts as well as Paul's letters, and the contexts of these confirms that James became a well-respected and important leader of the early church, and wrote the letter in the Bible that bears his name.