What Defines a True Christian?

Is there such a thing as a Deep Fake Christian? The problem of deep-fake Christians—those who act and sound like true followers of Jesus when their beliefs are actually different than what he taught—has been a real problem ever since the inception of the church. How can one tell what marks a true Christian from someone who has been corrupted by a deep fake? Is it simply a desire to follow Jesus, to follow the conviction of the Holy Spirit? As the Apostle John warned the local church in his day, we must be careful because there are wolves out there who like to dress as sheep and, as they say, The Devil's in the details.