Articles with professions/roles

Question

What is the right article for the professions/roles in such cases:

For example, we are talking about a racer as a “profession” or a “role”. Should I use “a” racer or just “racer” or “the” racer?

Examples:
Generally talking about the profession/role:
(A/The) racer should be able to relax.

Explaining what the role of the person is, for example, in a team, in general:
In a team, (A/The) Manager is the one who talks to people a lot.
The whole team contributes to the victory, not only (the?) racer himself.

Explaining what the person of such and such profession/role does, in general:
(A/The) free diver is (a/the) person who dives under the water.

Answer 1

In example 1, generally talking about the profession, you would use A.

In example 2, explaining what the role of the person is, you would use The.

In example 3, explaining what a person of a certain profession does, you can use either, although "the" implies that a free diver, in this case, is more specific than a regular diver.