"The wicked one", ho poneros, can refer to ordinary human beings. The phrase doesn't have to refer to a supernatural being. Consider how the Lord Jesus uses it in the Sermon on the Mount. He warns that men will do evil against us (Mt. 5:11). And He goes on to warn in Mt. 5:39: "Resist not the evil one; but whoever smites you on the one cheek, turn to him the other". The "evil one" simply referred there to an individual who did evil. God makes the sun rise upon 'the evil ones' as well as the good (Mt. 5:45- the same Greek phrase is used, although in the plural). He even refers to some in the audience hearing the Sermon on the Mount as being in that category: "You, being evil [Gk. 'wicked ones']" (Mt. 7:11). Yet within the Sermon, we find Jesus advising us to pray "Deliver us from the evil one" (Mt. 6:13). The evil ones, in the context of the Lord's Sermon, were the human beings whom He foresaw would persecuted His followers. The context gives no hint that the Lord had in view any supernatural being. His later teaching suggests that He saw the 'wicked ones' in the first context as being the Jews who persecuted His earliest followers. He called them 'evil ones' (Mt. 12:34), and He traces the root of their 'evil' to the wicked heart of man [the Biblical 'satan'] being allowed to function without opposition: "An evil man [s.w. "wicked one"] out of the evil treasure [of the heart] brings forth evil things" (Mt. 12:35). And so the Jews of the first century were an evil or wicked generation (Mt. 12:39,45; 16:4; Lk. 11:29; Jn. 7:7). The 'evil ones' were the Jews who were in opposition to the work of Jesus and the preaching of His message; we find the same phrase used about the Jews who opposed Paul's preaching in Acts 17:5. The AV translates the phrase as "certain lewd fellows", but again, poneros is used- 'evil ones' would be a fair translation. This is all the background for the Lord's teaching that there would be an 'evil one' who would sabotage His preaching of the Gospel, sowing weeds amongst the wheat (Mt. 13:19,38,49). John's Gospel tends to speak of "the world" with specific reference to the Jewish world of the first century. The Lord parallels that "world" with "the evil one" in Jn. 17:15: "I pray not that You should take them out of the world, but that You should keep them from the evil one".
John's letters use language in the same way as his Gospel record. When John writes of the wicked one not 'touching' the believer, he is surely alluding to the Lord's prayer of Jn. 17:15: "I pray not that You should take them out of the world, but that You should keep them from the evil one". When John writes of "the wicked one", he surely has in mind the same 'wicked ones' of the Gospel records- the Jewish opposition to the message of Jesus. And this was indeed what John was up against, as under Divine inspiration he wrote his letters to his converts who were being troubled by Jewish false teachers. We see in 1 Jn. 5:19 the same parallel between the world, and the wicked one- because "the whole world lies in the wicked one". It's likely that John came to personify those many 'wicked ones' as one 'wicked one'. But the context provided by the Gospels is of wicked men, adversaries, satans, to the Gospel; who were like that because they brought forth 'wicked things' from their 'evil heart' (Mt. 12:35). No supernatural being is in view here at all. John goes on to heighten the contrast in 1 Jn. 5:20: Those wicked one were 'in' the wicked world, but the believers were 'in' Christ: "The whole world lies in the power of the evil one. But we know that the Son of God came, and has given us an understanding so that we truly know him that is true; and we are in Him that is true, in His Son Jesus Christ". John's converts had come out from being in the Jewish world, and were now in Christ.