Okay, this one looks pretty obvious: Henry VI, Part 1 is names after the central character, Henry VI. But wait—it's not as simple as it looks. Which doesn't mean it's super complicated, just that there's a little more going on here than initially meets the eye.
The fact that this play is named after Henry VI positions it in contrast with his father Henry V (whom Shakespeare also gave the old theatrical treatment to), kind of the way that viewers think of Star Wars: A New Hope as being about Luke and Star Wars, Episode II as being about his father, Anakin. It also means that people will associate it with Shakespeare's other history plays, especially Henry VI, Part 2 and Part 3. In other words, when it comes to the name of this play, it's all about positioning it in a larger context.