i cant find a series of books that i read along time ago

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i read a series of books many years ago and i can't remember what they are called but i can only remember a few things about it. hopefully that will be enough. the main character i think was British and was a colonel or something, he goes into a mountain or through a portal or something and starts going through levels in a world or something and meets alies and enimies in weird forms such as clones, robots, and animals and at the end it turns out that he is the master of some sort of energy or something and can do anything. if you know or think you know what the series is no matter what you think tell me cus it was really good and i want to read it again.