“Gladiator” sounds like “glad he ate her,” and puns have been cited in print since at least 1836. A riddle was posted on the newsgroup rec.humor on July 13, 1992:
 
Q: What do you call a smiling Roman with pubic hair between his teeth?
A: Gladiator! (Glad he ate her)
 
Several jokes involve Spartacus (a famous Thracian gladiator) and cannibalism. “What did Spartacus do to the cannibal who ate his nagging wife? Nothing. He was gladiator” was posted on Twitter on December 23, 2017. “What did Spartacus say to the cannibal who killed his wife. Nothing, he’s Gladiator” was posted Reddit—Jokes on March 25, 2018.
   
         
Wikipedia: Spartacus
Spartacus (Greek: Σπάρτακος Spártakos; Latin: Spartacus; c. 111–71 BC) was a Thracian gladiator who, along with the Gauls Crixus, Gannicus, Castus, and Oenomaus, was one of the escaped slave leaders in the Third Servile War, a major slave uprising against the Roman Republic. Little is known about Spartacus beyond the events of the war, and surviving historical accounts are sometimes contradictory and may not always be reliable. However, all sources agree that he was a former gladiator and an accomplished military leader.
 
This rebellion, interpreted by some as an example of oppressed people fighting for their freedom against a slave-owning oligarchy, has provided inspiration for many political thinkers, and has been featured in literature, television, and film.
     
Google Books       
1836, The New Monthly Magazine and Literary Journal, pg. 365:
G;adiator in arena.”
“Translator!” sounded on all sides, when the ingenious gentleman explained that it arose from the destruction of a woman by a Roman, who devoured her, and then declared he was “glad he ate her in the arena.”
 
Google Books
29 July 1865, Harper’s Weekly (New York, NY), pg. 475, col. 4:
Why is a cannibal exulting after dining of a missionary’s wife like the finest race-horse of the present year?— Because he’s Glad-he-ate-her.
 
Google Groups: rec.humor
bad jokes  
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7/13/92
My younger sister told me this one…(don’t know where she heard it)
 
What do you call a smiling Roman with pubic hair between his teeth?
Gladiator! (Glad he ate her)
     
Urban Dictionary
Gladheateher
A happy roman lady-eater
How would you call a smiling roman arena fighter with pubic hair between his teeth ?
A G-LADY-eater
by Ruv March 19, 2005
 
Twitter 
wally
@wal_l_y
Q: in ancient rome times, what name they gave to a cannibal?A: gladiator (glad he ate her) ahahahahaha…!!!! ☺  http://myloc.me/5ATU
10:19 AM - 25 Jun 2009
 
Twitter 
The Angry Czeck
@angryczeck
VERY LITTLE KNOWN FACT: A cannibal gladiator is called a Glad-He-Ate-Her
12:42 AM - 3 Mar 2011
   
Twitter
The Bloody Oranges
@bloodyoranges
I strongly recommend Spartacus: Gods of the Arena if you like violence, boobies, wieners, oily pecs, boobies, and violence. #glad-he-ate-her
2:37 PM - 8 Mar 2011
 
Twitter
Brentley Wells
@B_M_Wells
Random fact - the term “gladiator” comes from the cannibal phrase: ‘glad he ate her’
9:49 AM - 8 Nov 2011
     
Twitter
Caleb Laue
@CalebLaue
What did Spartacus do to the cannibal who ate his nagging wife? Nothing. He was gladiator.
1:07 AM - 23 Dec 2017
 
Reddit—Dad Jokes
Spartacus (self.dadjokes)
submitted January 14, 2018 by Jackofgilead
What did Spartacus say to the cannibal who ate his wife?
Nothing. He was glad he ate her
 
Reddit—Jokes
What did Spartacus say to the cannibal who killed his wife.
submitted March 25, 2018 by LittEleven
Nothing, he’s Gladiator.
 
Twitter
LaffGaff
@LaffGaff
What did Spartacus say to the cannibal who killed his wife?
Nothing, he’s Gladiator.
#funny #jokes #jokeoftheday
5:12 PM - 28 Mar 2018