This is unfortunately an issue of job portrayal. The best way to get substandard work is to advertise that the position is a stopgap to deal with a temporary situation. As a start, I'd clarify that the emergency stage is over. He's still going to be working some issues on the team, and that gives everyone the opportunity to start following some standard best practices for here on out, so the emergency situation doesn't arise again. This does a lot of work--it acknowledges his contributions while making it clear that the work was substandard, while allowing him to save face for having a perfectly valid reason to do shoddy work. It also places the blame for the emergency on shoddy work he didn't do. This will all establish that moving forward things are different and allow him to reset. Most importantly, it gives you the opportunity to mentor him on building code correctly.

If you can do this without speaking with his boss, that's great. If you do need to bring him in the loop, I'd give the same narrative to the boss.

Don't overreact to a perception that you're being devalued due to his performance. Then you're giving credit to the idea. It's normal in all parts of the organization to get rock stars who can do wonderful things until the whole project blows up because of work quality. Take the leadership role here and it's likely everyone will simply let you have it.

This is unfortunately an issue of job portrayal. The best way to get substandard work is to advertise that the position is a stopgap to deal with a temporary situation. As a start, I'd clarify that the emergency stage is over. He's still going to be working some issues on the team, and that gives everyone the opportunity to start following some standard best practices from here on out, so the emergency situation doesn't arise again. This does a lot of work--it acknowledges his contributions while making it clear that the work was substandard, while allowing him to save face for having a perfectly valid reason to do shoddy work. It also places the blame for the emergency on shoddy work he didn't do. This will all establish that moving forward things are different and allow him to reset. Most importantly, it gives you the opportunity to mentor him on building code correctly.

If you can do this without speaking with his boss, that's great. If you do need to bring him in the loop, I'd give the same narrative to the boss.

Don't overreact to a perception that you're being devalued due to his performance. Then you're giving credit to the idea. It's normal in all parts of the organization to get rock stars who can do wonderful things until the whole project blows up because of work quality. Take the leadership role here and it's likely everyone will simply let you have it.