The Gospel of Matthew lists the 12 apostles in the following order: Simon (whom Jesus later renamed "Peter"), Andrew, James (the son of Zeb'edee), John, Philip, Bartholomew, Thomas, Matthew, James (the son of Alphaeus), Thaddaeus, Simon and Judas Iscariot. The names appear in different orders in the other gospels.
The Gospel of Mark lists the apostles in the order of Peter, James (the son of Zeb'edee), John, Andrew, Philip, Bartholomew, Matthew, Thomas, James (the son of Alphaeus), Thaddaeus, Simon and Judas Iscariot. The Gospel of Luke lists the apostles in an order similar to Matthew's, with a couple of differences. The order is Peter, Andrew, James, John, Philip, Bartholomew, Matthew, Thomas, James the son of Alphaeus, Simon, Judas (Thaddeus) and Judas Iscariot.
Although each list has a different order, they all name Simon Peter first. In Matthew 16:18-19, Jesus gave Peter a special place in the leadership of his church, although different Christian denominations debate the exact nature and extent of this leadership.
Judas Iscariot, who always appears last in the lists, betrayed Jesus in the Garden of Gethsemane and subsequently hanged himself, according to the Gospel of Matthew. Because of this, the Book of Acts records the Apostles selecting Matthias to replace Judas Iscariot.