“Him who has been from the beginning” could be a name of God or a name of Jesus (Yeshua‘). The reference to God as Father later in the passage suggests that this name points to Jesus. Part of the emphasis of John’s first letter is that Jesus shares God’s divinity, so the name applies equally to Father and Son. In the book of Hebrews Jesus is called “He who has no beginning of days or end of life” (Heb. 7:3).
Him who has been from the beginning in Greek:
Ho ēn ap’ archēs
Strong’s Concordance numbers: 1510, 746
Bible references: 1 John 1:1; 2:13-14
I am writing to you, fathers, because you know Him who has been from the beginning. I am writing to you, young men, because you have overcome the evil one. I have written to you, children, because you know the Father. I have written to you, fathers, because you know Him who has been from the beginning. I have written to you, young men, because you are strong, and the word of God abides in you, and you have overcome the evil one. (1 John 2:13-14)
Similar names for God and Jesus are: Him who lives forever and ever, the Beginning and the end, and the Beginning of the creation of God.