"Who is faster?"

Translation: Ποιος είναι γρηγορότερος;

[Ari654900]

would γρηγοτερος mean "the fastest" and γρηγοροτερος "faster"?

[mizinamo]

γρηγορότερος - faster

ο γρηγορότερος - the fastest

The difference is that one has the definite article.

γρηγότερος does not exist because γρηγός doesn't.