Satan appears across all strata of New Testament tradition: tempting Jesus in the wilderness (Matthew 4:1-11), entering Judas (Luke 22:3), asking to sift Peter like wheat (Luke 22:31), blinding unbelievers to the gospel (2 Corinthians 4:4), and ultimately being bound and then cast into the lake of fire (Revelation 20). Jesus witnessed his fall "like lightning from heaven" (Luke 10:18) and declares him "the ruler of this world" who has no claim on Jesus (John 14:30). His final defeat is certain (Romans 16:20: "the God of peace will soon crush Satan under your feet").
Satanas is a transliteration of the Hebrew satan (adversary, accuser). It designates the chief spiritual opponent of God and humanity — the tempter, accuser, deceiver, and destroyer. Jesus treats Satan as a personal being of great but limited power.