High Protector

Lord High Protector was a title given to Megatron. It is unknown why Optimus Prime wasn't given the title. It could also be because Megatron was older or more powerful, as in the movie, Megatron flings Optimus around and his dual plasma cannons caused Prime to be flund across the street while Prime's merely caused Megatron's to spin around.

From Teletraan I: The Transformers Wiki, a Wikia wiki.