It's unfortunate that some people don't believe there's an adversary called Satan, the devil. Some people don't even want to talk about him; they say, "There's no devil", trying hard to convince themselves in their delusion. Jesus didn't deny the existence of Satan, though He emphasized his defeat and our triumph over him.
Satan is real; he's a spirit being. He's not an illusion as some believe; he's a personality; an evil personality. He was an angel, according to the Bible, but he fell from grace and became the devil.
God didn't create a devil. He made an angel called Lucifer, son of the morning. However, through pride, he lost his position, was overthrown, and became the devil. So, Satan does exist; the Bible says he moves from one place to another: "And the Lord said unto Satan, Whence comest thou? Then Satan answered the LORD, and said, From going to and fro in the earth, and from walking up and down in it" (Job 1:7).
Although he has his demons running rampage all over the place, Satan isn't everywhere at the same time; he's not omnipresent, and doesn't know everything. To counter him, the Bible says you're to resist him steadfastly in the faith (1 Peter 5:8-9). That's how you keep him on the run (James 4:7). As long as you operate in faith, Satan cannot withstand you; you're superior to him.
When Jesus defeated Satan in hell, you were in Him. In Christ, you defeated Satan and his cohorts of hell. Now, you're seated with Christ in the heavenly realms, far above all principality, and power, and might, and dominion, and every name that is named, not only in this world, but also in that which is to come (Ephesians 1:21). So, Satan is under your feet. Though he's not an illusion, he's not a factor in your life.