It sounds like Mighty Max.
From Wikipedia: Characters include
Max (voiced by Rob Paulsen) – The hero of the series, Max is a
rambunctious young teenager who is very good at getting out of (and
into) trouble. One day, he receives a mysterious package containing a
videotape and a red baseball cap with a large, yellow "M" on it. The
cap is actually an ancient key to various portals found throughout
time and space
This matches your first character pretty perfectly.
Virgil (voiced by the late Tony Jay) – The last living Lemurian,
the next step in human evolution, as revealed in one episode. The
Lemurians either created or discovered the portals, and later created
the key in order to access them. Having a bird-like appearance, the
Lemurians valued knowledge above all else and compiled the most
extensive library the world has ever known.
Evolved, birdlike human.
Norman (voiced by Richard Moll) – Max's bodyguard. In the time of
the early Vikings, a young Norman watched his father die at the hands
of Spike, an indestructible deranged and bloodthirsty warrior. Because
of his size at the time, Norman couldn't help when he had the chance
(he was unable to lift his father's war-axe), and thus blamed himself
for the tragedy; at his father's grave, he vowed to become the
greatest warrior that ever lived (cf. "Norman's Conquest"). The
only creatures which give him pause for terror are spiders. In the
show he meets several of tremendous size and strength.
Not quite a gladiator, but big and brawny.
Fanart of the three: