One of those days Jesus went out to a mountainside to pray, and spent the night praying to God. When morning came, he called his disciples to him and chose twelve of them, whom he also designated apostles: Simon (whom he named Peter), his brother Andrew, James, John, Philip, Bartholomew, Matthew, Thomas, James son of Alphaeus, Simon who was called the Zealot, Judas son of James, and Judas Iscariot, who became a traitor. - Luke 6:12-16

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The term apostle comes from the Greek ἀπόστολος or apostolos a word formed from the combination of apo (from) and root stello (I send, I depart) originally meaning messenger or delegate.  The original twelve were called by Christ with Saint Matthias replacing Judas after his betrayal. All twelve were eventually martyred with only Saint John surviving into old age.