5 And from Jesus Christ, who is the faithful witness, and the first begotten of the dead, and the prince of the kings of the earth. Unto him that loved us, and washed us from our sins in his own blood,
This term "first begotten" is derived from the Greek word "prototokos" which is defined as follows:
4416 prōtótokos (from 4413 /prṓtos, "first, pre-eminent" and 5088 /tíktō, "bring forth") – properly, first in time (Mt 1:25; Lk 2:7); hence, pre-eminent (Col 1:15; Rev 1:5).
This word occurs three times in the Bible, two of which occur in Colossians and I think a look at that passage will be helpful in understanding some of what we will encounter later in Revelation.
Col 1: 12Giving thanks unto the Father, which hath made us meet to be partakers of the inheritance of the saints in light:
13Who hath delivered us from the power of darkness, and hath translated us into the kingdom of his dear Son:
14In whom we have redemption through his blood, even the forgiveness of sins:
15Who is the image of the invisible God, the firstborn of every creature:
16For by him were all things created, that are in heaven, and that are in earth, visible and invisible, whether they be thrones, or dominions, or principalities, or powers: all things were created by him, and for him:
17And he is before all things, and by him all things consist.
18And he is the head of the body, the church: who is the beginning, the firstborn from the dead; that in all things he might have the preeminence.
19For it pleased the Father that in him should all fulness dwell;
20And, having made peace through the blood of his cross, by him to reconcile all things unto himself; by him, I say, whether they be things in earth, or things in heaven.
In Rev 1:5 He is referred to as "the first begotten of the dead" whereas in Col 1:15 He is referred to as "the first born of every creature." The significance of what is said here will gain added importance as we move forward in Revelation.