Where did the "dog" come from?

Question

In I Am Number Four when John (Number Four) and Henri are moving from the beach to Paradise, they are being followed by a lizard which then transforms into a dog and gets adopted by them.

Later on the dog transforms into some kind of monster dog and helps John during the attack of the Mogadorians.

It was never really clear to me where the dog came from. All the movie explains about it is when Number Six says something along the lines of

Yeah, he's a shape shifter and has been following you. Somebody had to protect you after all.

That doesn't really answer anything.

1. Where did the dog come from? Has he been following John from the beach? Or even his whole life?
2. Who sent him and why? John alread had a protector.
3. How did Six even who the dog was or how long he had been following him? She had no clue where Number Four was until he appeared on Youtube.

Maybe I am reading too much into it, but the dog was presented as an important clue throughout most of the movie and then just shrugged off as: "Well yeah, it's a shapeshifting dog that protects you, no biggie."

Answer 1

From Wikipedia:

John, Sarah and Sam are attacked by the Mogadorians, who brought two giant monsters to hunt the trio. They are saved by Number Six and Bernie Kosar. Number Six reveals that Bernie Kosar is a Chimera that can shapeshift and was sent by John's biological parents to protect him.

There is more information about the "dog" in the novel series wikia.