The fast-food chain's costumed "King" escorted Mayweather to the boxing ring ahead of the fight.
It was an expensive and controversial endorsement for the company.
ICYMI: Burger King paid for king to walk in with Floyd Mayweather. Estimated to cost $1M+ pic.twitter.com/hCj6TCEC42
- Darren Rovell (@darrenrovell) May 4, 2015
"Brands have, for the most part, stayed away from Mayweather over the years precisely because of his public image," Fortune's Daniel Roberts reports. "He has three times in a row topped the Fortunate 50, our Sports Illustrated/Fortune athlete earnings list - all with zero outside endorsement deals."
Hundreds of people slammed Burger King on social media for standing with Mayweather.
So why would the company pay so much money for such a risky association?
In response to that question, a Burger King spokesman told Fortune, "We don't call him the King for nothing," referring to its mascot. The spokesman declined further comment.
According to Amobee Brand Intelligence, Burger King "got over a week's worth of publicity, just by sticking their mascot in the background of a shot at a high profile sporting event," AdWeek's Lost Remote reports.
Buzz around Burger King increased 1,343% on May 3, the day of the fight, compared to the previous day, according to the firm.
But it was mostly negative publicity.
Hundreds of people have slammed Burger King on social media for standing with Mayweather.
Burger King loves domestic violence . @BurgerKing
- hugh acheson (@HughAcheson) May 3, 2015
Not going to eat @BurgerKing again. Didn't know they condoned domestic violence like they do. What a shame! They should be embarrassed
- Eric Fries (@friesew) May 5, 2015
Has Burger King explained why they support a man convicted of domestic violence yet? Or tried to distance themselves from that taking place?
- Rob Engelsman (@rcengelsman) May 3, 2015
Good job at supporting domestic violence burger king. #terriblebranding
- Brandon Wenerd (@brandonwenerd) May 3, 2015
Umm @BurgerKing, why is your King walking to the ring with a wife beater? Do you support violence/abuse against women now? #badform
- Miss Envy (@missenvy) May 3, 2015
Burger King supports domestic violence, boycott Burger King!
- Ricksmith (@Ric_Moon) May 3, 2015