Short answer
Most evangelicals identify the author of 1 John (and therefore the speaker of 1 John 4:11–12) as the Apostle John — the “beloved disciple” who followed Jesus closely, traditionally also credited with the Gospel of John and the Johannine letters. He is seen as an eyewitness apostle whose pastoral, theological teaching carries apostolic authority.

Who he is (brief bio)
– John, son of Zebedee and brother of James, was a Galilean fisherman called by Jesus (Mark 1:19–20).
– He belonged to Jesus’ inner circle (Peter, James, John) and is traditionally identified as the “disciple whom Jesus loved” (e.g., John 13:23; 19:26; 21:7,20).
– Early Christian tradition (Irenaeus, Clement of Alexandria, Tertullian) locates him in Ephesus late in the first century, where he taught and wrote. Many evangelicals hold that he lived to old age and wrote from Asia Minor.

Why evangelicals accept John as the author
– Internal affinities: 1 John shares distinctive vocabulary and theology with the Gospel of John (themes like “love,” “light / darkness,” “abiding,” and high Christology — God revealed in Jesus).
– Eyewitness claim and apostolic authority: Evangelicals value the link to an eyewitness apostle because it grounds the letters’ teaching and pastoral exhortations in what Jesus actually revealed.
– Early church testimony: Several early church fathers attribute the Gospel and the epistles to John the Apostle, which evangelicals accept as weighty historical testimony.

Context and purpose of 1 John (relevant to 4:11–12)
– 1 John was written to combat false teaching (often labeled proto-Gnosticism or Docetism) that denied Jesus’ full incarnation and/or emptied Christian life of real moral demands.
– The letter emphasizes assurance of salvation, true fellowship with God, and the practical evidence of authentic faith — chiefly love for other Christians. 1 John 4:11–12 fits this pattern: because God loved us in Christ, we must love one another; love is the visible sign that God’s presence is real among us.

Theological emphases behind the verses
– God’s initiative: God’s love is prior and decisive — we love because God first loved us (1 John 4:10–11).
– Visibility of God in community: “No one has seen God; if we love one another, God lives in us and his love is perfected in us” (4:12). For evangelicals, this underscores both the incarnation (God revealed supremely in Christ) and the ethical outworking of that revelation in the church.
– Pastoral and practical: The apostle appeals to believers’ everyday relationships as the test and display of gospel truth.

Typical dating and location (evangelical consensus)
– Most evangelicals date 1 John to the late first century (roughly AD 85–95) and place its composition in Ephesus or nearby regions of Asia Minor, though some conservative scholars argue for an earlier date. The exact dating does not, for most evangelicals, undermine Johannine apostolic authorship or authority.

Application (how evangelicals generally use this)
– As apostolic teaching, 1 John is authoritative for doctrine and ethics: it grounds Christian love in God’s redemptive action in Christ and calls the church to show God’s reality by loving one another.
– It is frequently used in pastoral teaching on assurance of salvation, unity, and practical discipleship.

If you want, I can:
– Quote 1 John 4:11–12 and briefly unpack each phrase line by line.
– Give short summaries of evangelical commentaries on 1 John (e.g., Leon Morris, John Stott, D. A. Carson, Andreas Kostenberger).