Character description from
wookieepedia,
https://starwars.fandom.com/wiki/Re
x

"Rex, designation CT-7567, was a
veteran
Clone Captain, Advanced Recon
Commando,
and eventual Clone Commander who
commanded the Grand Army of the
Republic's
famed 501st Legion of clone troopers
during
the Clone Wars. Rex later served as a
captain
and commander within the Alliance to
Restore
the Republic during the Galactic Civil
War.
Rex
participated in many battles over the
course of
the Clone Wars. As the captain of the
501st,
Rex served as second-in-command to
Jedi
General Anakin Skywalker, whose
bravery
and
unconventionality in battle he came
to
share.
In addition to being a close friend of
Skywalker he also became friends
with
Skywalker's apprentice, Ahsoka Tano.
He
was
close with Marshal Commander Cody,
with
their relationship mirroring that of
their
respective Jedi Generals, Skywalker
and
Obi-
Wan Kenobi, whom Rex was also well
acquainted with. Rex and his
companions
often worked together during the
front-line
campaigns against the Confederacy
of
Independent Systems."

Costume description:
Armor is made to mirror Captain
Rex's
animated look from seasons 4-7.