Karna. Nobunobu can gimmick him out with her strong anti-Mystery stuff. Queen of the Amazons was able to give him a run for his money in Strange Fake.
He's free to Sakura's vagina, too.
Also all non-surfing Mo-sans a shit.
This is how I Chaos Lord
Jonathan Walker
Aaron Powell
There aren't really characters who are strictly speaking stronger than him other than the Aristoteles (the Types, the embodied apex of their celestial body's conceptual nature). There are characters who aren't super old Servants who probably have a "good match up" against him, but this is largely a matter of Gilgamesh being an utter retard who never comes out swinging his full strength and them incidentally fighting in a way that may be able to circumvent GoB long enough to catch him off guard and deal an unexpectedly decisive blow.
Austin Scott
Enkidu as Divine Beast (Berserker), Solomon, Herakles (in Archer, also as Alcides).
That's basically it.
Wyatt Clark
Apparently According to GW and ADB it is.
Elijah Johnson
...
Gavin Jones
I didn't think the Japs knew about Star Wars.
Caleb Clark
Are you kidding? They fucking love Star Wars. If anything it's probably only slightly less big in Moonland as 'Murrica.
Daniel Lee
Kazane Aoba could give him a run for his money.
Benjamin Torres
Fate/Grand Keijo would be amazing
Carson Jackson
They probably see the jedi as space samurai
Which isn't exactly wrong to be honest