Short answer
Most evangelicals identify the author of 1 John (and therefore the author behind 1 John 4:18) as the Apostle John — the “beloved disciple” of Jesus, also traditionally credited with the Gospel of John and the other Johannine epistles. This view is based on the letter’s close theological and linguistic affinity with the Fourth Gospel and on early church testimony.

Who John was (as understood in evangelical circles)
– John, son of Zebedee, was one of the Twelve and part of Jesus’ inner circle (with Peter and James).
– He is often called the “beloved disciple” in the Gospel of John and is traditionally identified as its author.
– Early Christian writers (e.g., Irenaeus, Clement of Alexandria) attribute the Fourth Gospel and the epistles to John the Apostle. Evangelicals generally accept this traditional attribution.

Why evangelicals accept John as the likely author
– Vocabulary and themes: 1 John shares distinctive words and themes with the Gospel of John (light/darkness, love, eternal life, Son of God, Spirit), suggesting a common author or circle.
– Theological perspective: the high Christology and emphasis on incarnational truth that combats denial of Christ’s flesh (proto‑docetism/gnostic tendencies) match what the Fourth Gospel addresses.
– Early church testimony and consistent manuscript tradition favor Johannine authorship.
– The letter’s pastoral tone and claims of eyewitness authority fit the profile of an apostle who knew Jesus personally.

Brief exegesis of 1 John 4:18 from an evangelical standpoint
– Text (NIV paraphrase): “There is no fear in love. But perfect love drives out fear, because fear has to do with punishment. The one who fears is not made perfect in love.”
– Key points evangelicals draw from it:
– “Perfect/complete love” (Greek: téleia agápē) refers to God’s perfect, saving love shown in Christ’s atoning work.
– When a believer knows and rests in God’s love via faith in Christ, the fear of final judgment and condemnation is overcome — this gives assurance of salvation.
– True knowledge of God’s love produces both assurance and transformed living: love for God and others is the fruit and test of genuine faith (not antinomian license).
– The passage ties doctrine (who Jesus is and what he accomplished) to experience (assurance and love), which is characteristic of John’s pastoral aim: to combat false teaching and to assure believers of eternal life.

Pastoral application
– Use the verse to encourage Christians toward both assurance and obedience: assurance that Christ’s love removes ultimate fear, and motivation to grow in love as evidence of genuine faith.
– Emphasize Christ’s substitutionary atonement and the present work of the Spirit in producing love and confidence before God.

If you want, I can:
– Give a short biographical sketch of John with patristic citations (Irenaeus, Clement), or
– Walk through 1 John 4:7–21 verse‑by‑verse showing how verse 18 fits the argument.