The Antichrist refers to a specific person who will appear at the end of the present age (just before Christ returns), and will be the embodiment or fulfillment of all evil. The word "Antichrist" literally means "someone who is opposed to Christ" -- and that's exactly what the antichrist will be: absolutely opposed to Christ and His people.
Although the Bible doesn't go into detail, it's clear that the Antichrist will be part of Satan's final attempt to stop God's plan for the world. Remember: Satan is totally opposed to God, and his only goal is to block God's plans in every way he can. He attempted it at the beginning of the human race with Adam and Eve, and again (although unsuccessfully) at the beginning of Jesus' ministry (see Matthew 4:1-11). As the time approaches for Jesus' return, Satan will make one final, full-scale attempt to deceive the world and turn people away from Christ.
Is the Antichrist alive today? The Bible tells us not to speculate about this -- but it does urge us to be alert and on guard. It also reminds us that Satan is always active, and "as you have heard that the Antichrist is coming, even now many Antichrists have come" (1 John 2:18).
When he comes, the Antichrist will claim to be God -- but he also will deny the truth of Christ and oppose those who follow Him. The key is to know God's truth . . . believe God's truth . . . and live by God's truth. Remember: "Resist the devil, and he will flee from you. Come near to God and he will come near to you" (James 4:7-8).