They're called Deep Fakes. They're videos that have been manipulated with high tech methods to make someone famous say something they never said. A voice actor says something different. Then computers make the person's mouth match what they say. This was done famously with Obama and Jordan Peele (see the bottom of this blog).
Someone did a great job with this video from Game of Thrones. In this one, Jon Snow apologizes for the highly criticized final season.
Here's the Obama deep fake.