Who are those who are asleep in 1 Thessalonians 4?

Who are those Paul's describes as “asleep” in 1Thessalonians 4?

Paul writes to the church in Thessalonica saying:

1Th. 4:13 But we do not want you to be uninformed, brethren, about those who are asleep, so that you will not grieve as do the rest who have no hope.
1Th. 4:14 For if we believe that Jesus died and rose again, even so God will bring with Him those who have fallen asleep in Jesus.
1Th. 4:15 For this we say to you by the word of the Lord, that we who are alive and remain until the coming of the Lord, will not precede those who have fallen asleep.
1Th. 4:16 For the Lord Himself will descend from heaven with a shout, with the voice of the archangel and with the trumpet of God, and the dead in Christ will rise first.
1Th. 4:17 Then we who are alive and remain will be caught up together with them in the clouds to meet the Lord in the air, and so we shall always be with the Lord.
1Th. 4:18 Therefore comfort one another with these words.

In v.13 Paul uses the word “asleep” as a polite way of describing death, in the same way we might say someone has “passed away” rather than saying the person has died. Therefore, those who are “asleep” in 1Thess 4 are those Christians who have died. By the context, we see Paul was referring to believers who die prior to Christ’s coming for the Church at the Rapture.

For a complete explanation of this passage, please read "How do we know there will be a Rapture."