-moderator-

meaning:
noun [C]
1 (US USUALLY mediator) FORMAL someone who tries to help other people come to an agreement:An independent moderator should be appointed to oversee the negotiations.

2 US someone who makes certain that a formal discussion happens without problems and follows the rules:
He challenged the president to a series of TV debates. Just the two of them, with no moderator.

3 UK SPECIALIZED someone who makes certain that all the people marking an exam use the same standards:The final marks awarded for coursework will depend upon the moderator.

She was a moderator for the 2007 Global Conferenceon Buddhism.