A person who announces someone entering a room is often referred to as a "master of ceremonies" (MC) or simply an "announcer." In formal settings, such as events or ceremonies, this role may also be called a "host" or "emcee." Their primary function is to introduce individuals and maintain the flow of the event.
Presenter
Town crier, mayor or council.
no
A passenger? a vehicle user?
The person is a blackmailer.
can you call someone a welth of knowledge
a person
A person?
You call that person a scholar.
There would be a number of names a person could be called. The primary one would be competitor. However, it could be skier, bobsledder, or ice skater.
You would call them someone who peruses.
an ally