If they all went after him then you might want to try a phased introduction. Where you put them with him one at a time. How did they act towards the hen?
Being kept in a coop for a few days to a week resets where home is for most chickens. The period of see but no touch during the introduction serves that propose well.
The method I would use is have them in a cage or partitioned off part of the run for a few days, the let them free range with the rest. With the large space when they free range they can get away from the ones pecking them. Leaving them sleep in the separate area for a few more. If all is...