How to deal with a player that prioritizes combat over roleplay in a roleplay heavy campaign?

Question

How can I deal with a player that prioritizes combat over roleplay in a roleplay heavy campaign? They all knew what they were getting into and agreed during the session 0.

He tends to try and rush other players through roleplay and investigation and only focus on combat. He would interrupt another player while they were asking good questions to try and get to the point quicker. I can't really say it's part of his character because his roleplay for the character changes every week (inconsistent). There were a few occasions where he would 'Leroy Jenkins' during discussion (he would stop discussion and run into the dungeon alone).

This is counterproductive as the combat is often lethal and the investigation is crucial to lowering the difficulty. I'm worried that I will have to either make the combat easier or remove more roleplay to avoid player deaths or loss of interest. This would reduce the over all quality (and gimmick) of the campaign.

It's only 1 out of the 3 players that is like this, but he tends to pressure the others, and the other players brought this up to me.

Answer 1

What do they really want?

You say that everyone agreed to this in the session 0, which is great. This means everyone was aware of what you want, they jumped on board and ostensibly also want that thing. I've had one of these people before and the key is to find out what they really want. They agreed to a role-play heavy campaign, but you might want to pull them aside and ask why they're so focused on combat. Do you still exclusively award XP via combat? If so you might want to consider changing that. The player might be fine with a role play heavy game, but what they really want is to engage the reward structures of the game. Magic items, XP, that kind of thing.

But what if they just want to kill?

Well, if they're being blood thirsty for the sake of it (or for the sake of using the other 85% of the game rules) you'll have to have a different conversation. If this players pressure to kill things is making the rest of the players (The DM is a player too) have less fun you'll have to seriously consider that maybe this player isn't a good fit for your current campaign idea. Sometimes that happens, but it's okay. If they're an adult they'll realize what they've done wrong and be okay with waiting for the next campaign that contains more combat, or they'll change so that everyone can have equal amounts of fun during the current campaign.

TL;DR

All in all, it still comes down to talking to them. You have to find out what they really want, and decide if you can accommodate them or have them sit out until the next campaign.