Coworker is stealing as many people's jobs as he possibly can

I have a co-worker that comes in 3 hours early. He works every single day including weekends and holidays. He NEVER takes a day off and he thinks he runs the place. Over the last couple of years, he has been taking over more and more responsibilies, including some of mine. I'm getting really fed up with him taking over people's responsibilies without even asking them if they need help. I've talked with management about this but they just turn a blind eye.

Has anyone else experienced something like this?

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