For pre-tribbers let's keep this simple. Who are these people?

Rev 20:4 And I saw thrones, and they sat upon them, and judgment was given unto them: and [I saw] the souls of them that were beheaded for the witness of Jesus, and for the word of God, and which had not worshipped the beast, neither his image, neither had received [his] mark upon their foreheads, or in their hands; and they lived and reigned with Christ a thousand years.

Rev 20:5 But the rest of the dead lived not again until the thousand years were finished. This [is] the first resurrection.