Agent noun of discipline: one who disciplines.(noun)
Wiktionary.org : Text is available under the Creative Commons Attribution-ShareAlike License
Use "discipliner" in a sentence
"But respect for the discipliner was lost and negative attitudes developed toward the organization."
"And yet if you know you're going to have to handle obstreperous congresspersons of your own party, you just might go for a known leader and discipliner of congressional Democrats."
"We often talk about the dangers of ideology, but the fact is that one thing idealogy is, is a tremendous intellectual discipliner that prevents you from saying contradictory things all the time."