Saint Andrew in the Christian Bible is the earliest disciple of Jesus and one of the twelve Apostles.

The Gospel of John states that Andrew was a disciple of John the Baptist, whose testimony first led him, and another unnamed disciple of John the Baptist, commonly thought to be John the Evangelist to follow Jesus.[Jn. 1:35-40] Andrew at once recognized Jesus as the Messiah, and hastened to introduce him to his brother.[Jn. 1:41] Thenceforth, the two brothers were disciples of Christ.

On a subsequent occasion, prior to the final call to the Apostolate, they were called to a closer companionship, and then they left all things to follow Jesus.

In the gospels, Andrew is referred to as being present on some important occasions as one of the disciples more closely attached to Jesus, Andrew told Jesus about the boy with the loaves and fishes (John 6:8), with Philip told Jesus about the Greeks seeking Him (John 12:20), and was one of four (the others being Peter, James, and John) to hear Jesus' teaching about what would soon happen (Mark 13:3).

Eusebius quotes Origen as saying Andrew preached along the Black Sea as far as the Volga, Kiev and Novgorod.

Hence he became a patron saint of Ukraine, Romania and Russia.

According to tradition, he founded the See of Byzantium (Constantinople) in CE 38, installing Stachys as bishop.

According to Hippolytus of Rome, he preached in Thrace, and his presence in Byzantium is also mentioned in the apocryphal Acts of Andrew, written in the second century; Basil of Seleucia also knew of Apostle Andrew's mission in Thrace, as well as Scythia and Achaia.

This diocese would later develop into the Patriarchate of Constantinople.

Andrew is recognized as its patron saint.

Andrew is said to have been martyred by crucifixion at the city of Patras (Patræ) in Achaea, on the northern coast of the Peloponnese.

Early texts, such as the Acts of Andrew known to Gregory of Tours, describe Andrew as bound, not nailed, to a Latin cross of the kind on which Jesus is said to have been crucified; yet a tradition developed that Andrew had been crucified on a cross of the form called Crux decussata (X-shaped cross, or "saltire"), now commonly known as a "Saint Andrew's Cross"— supposedly at his own request, as he deemed himself unworthy to be crucified on the same type of cross as Jesus had been.