The twenty-four elders had earlier used this same title in Revelation 11:17. It is an abbreviation of the name John used in Revelation 1:4: “who is and who was and who is to come.” In the present case the future dimension is lacking because the emphasis lies on God's being unchangingly faithful in the present plague to the promise given centuries ago. People may know that there are no surprises with him.
5 And I heard the angel in charge of the waters say, “Just are you, O Holy One, who is and who was, for you brought these judgments.