One of the two which heard John speak, and followed him, was Andrew, Simon Peter's brother.

People's New Testament

1:40 One of the two... was Andrew. Afterwards an apostle. He has the honor of being one of the first two disciples of Jesus.

Jamieson-Fausset-Brown Bible Commentary

40. One . was Andrew-The other was doubtless our Evangelist himself. His great sensitiveness is touchingly shown in his representation of this first contact with the Lord; the circumstances are present to him in the minutest details; he still remembers the Very hour. But "he reports no particulars of those discourses of the Lord by which he was bound to Him for the whole of His life; he allows everything personal to retire" [Olshausen].

Peter's brother-and the elder of the two.

Matthew Henry's Concise Commentary

1:37-42 The strongest and most prevailing argument with an awakened soul to follow Christ, is, that it is he only who takes away sin. Whatever communion there is between our souls and Christ, it is he who begins the discourse. He asked, What seek ye? The question Jesus put to them, we should all put to ourselves when we begin to follow Him, What do we design and desire? In following Christ, do we seek the favour of God and eternal life? He invites them to come without delay. Now is the accepted time, 2Co 6:2. It is good for us to be where Christ is, wherever it be. We ought to labour for the spiritual welfare of those related to us, and seek to bring them to Him. Those who come to Christ, must come with a fixed resolution to be firm and constant to him, like a stone, solid and stedfast; and it is by his grace that they are so.