Short answer
– The superscription of Psalm 86 identifies the author as King David. From an evangelical Christian perspective, David is therefore the most likely author of Psalm 86 and its statements (including v. 5).

Who David is (brief)
– David was the shepherd-boy who became Israel’s second king, a warrior, a poet and musician (traditionally the principal psalmist), and a central figure in God’s covenant promises to Israel (the “house of David” promise). Evangelicals view him as a historical, God‑called ruler described in 1–2 Samuel and as a repentant sinner (“a man after God’s own heart”) whose life experience deeply shaped his prayers and praise.

Why evangelicals accept Davidic authorship
– The psalm’s superscription explicitly names David, and the content (personal appeal in a time of trouble, intimacy with God, themes of sin/forgiveness and covenant trust) fits his life and voice.
– Evangelical trust in the reliability of the biblical text and its traditional attributions leads most evangelical scholars and pastors to accept Davidic authorship unless there is strong internal reason to doubt it.

What Psalm 86:5 says and means (theological points)
– Common renderings: KJV — “For thou, Lord, art good, and ready to forgive; and plenteous in mercy unto all them that call upon thee.” NIV — “You, Lord, are forgiving and good, abounding in love to all who call to you.”
– Key themes: God’s essential goodness, His readiness to forgive, and His overflowing mercy/loving‑kindness toward those who call on Him.
– “Call on” expresses prayerful dependence. The verse emphasizes both God’s character (good, merciful) and the proper human response (calling on God, trusting Him).

Evangelical application and significance
– Assurance of forgiveness: This verse gives believers confidence that God is disposed to forgive when we repent and call on Him — a confidence grounded in God’s character.
– Gospel connection: Evangelicals see God’s mercy culminating in Jesus Christ. The Old Testament promises of forgiveness and steadfast love find their fullest fulfillment in Christ’s atoning work; calling on the Lord for mercy ultimately points to faith in Christ (cf. Romans 10:13).
– Prayer and devotion: Psalm 86 is modeled as a personal, humble prayer in distress — a pattern for believers to pursue honest supplication, confession, and trust.
– Pastoral use: Good for teaching about God’s readiness to forgive, for comforting sinners who repent, and for encouraging prayerful dependence in trials.

Context of Psalm 86 (brief)
– The psalm is a prayer for help and protection, mixing lament with praise and trust. It sounds like a king in distress appealing to God’s covenant faithfulness; historically, evangelicals take it as an authentic Davidic prayer composed in one of his times of trouble.

Practical takeaway
– If you’re struggling with guilt or fear, Psalm 86:5 invites you to call on God with confidence in His goodness and mercy. For Christians, it points to the gracious provision of forgiveness in Christ and the proper posture of humble dependence before God.

If you want, I can:
– Provide a short devotional based on Psalm 86:5,
– Compare several translations,
– Or summarize evangelical commentaries on Psalm 86.