Maximilian Adelbert Baer (February 11, 1909 – November 21, 1959) was an American professional boxer and the world heavyweight champion from June 14, 1934, to June 13, 1935. He was known in his time as the Livermore Larupper and Madcap Maxie. He had a record of 68-13. 

Two of his fights (a 1933 win over Max Schmeling and a 1935 loss to James J. Braddock) were rated Fight of the Year by The Ring magazine. Baer was also a boxing referee, and had occasional roles in film and television. He was the brother of heavyweight boxing contender Buddy Baer and father of actor Max Baer Jr. Baer is rated #22 on The Ring magazine's list of 100 greatest punchers of all time.

On June 8, 1933, Baer fought and defeated German heavyweight and former world champion Max Schmeling at Yankee Stadium, by technical knockout. Schmeling was favored to win and was Adolf Hitler's favorite boxer. The Nazi tabloid Der Stürmer publicly attacked Schmeling for fighting a non-Aryan, as Baer's father was Jewish, calling it a "racial and cultural disgrace."

Although the Great Depression, then in full force, had lowered the income of most citizens, sixty thousand people attended the boxing match. 

NBC radio updated millions nationwide as the match progressed. Baer, who was of half Jewish descent, wore trunks which displayed the Star of David, a symbol he wore in all his future bouts. During the match, he dominated the rugged Schmeling into the tenth round, when Baer knocked Schmeling down and the referee stopped the match.

Columnist Westbrook Pegler wrote about Schmeling's loss, "That wasn't a defeat, that was a disaster", while journalist David Margolick claimed that Baer's victory would come to "symbolize Jewry's struggle against the Nazis."

Baer became a hero among Jews and those who despised the Nazis. According to biographer David Bret, after the war ended, it was learned that Schmeling had, in fact, saved the lives of many Jewish children during the war while still serving his country.

Film star Greta Garbo considered Baer's defeat of Schmeling to be a "mini victory" over Nazism, and she invited Baer to visit her while she was filming Queen Christina in Hollywood.

However, Baer's presence on the set was considered a "sacrilege" in Hollywood, as even MGM studio's head, Louis B. Mayer, wasn't allowed on Garbo's set, since she demanded total privacy while acting. Their friendship led to a romance, which lasted until he returned to New York to train for his next match against Primo Carnera.

On June 14, 1934, at the outdoor Madison Square Garden Bowl at Long Island City, New York, Baer defeated the huge reigning world champion Primo Carnera of Italy, who weighed in at 267 pounds. Baer knocked down the champion 11 times before the fight was stopped in the eleventh round by referee Arthur Donovan to save Carnera from further punishment. 

All the knockdowns occurred in rounds one, two, ten and eleven, which Baer thoroughly dominated. The intervening rounds were competitive. There is some dispute about the number of knockdowns scored, as Carnera slipped to the canvas on several occasions and was wrestled to the canvas other times. Despite this dominant performance over Carnera, Baer would hold the world heavyweight title for just 364 days.

On June 13, 1935, one of the greatest upsets in boxing history occurred in Long Island City, New York, as Baer fought down-and-out boxer James J. Braddock in the so-called Cinderella Man bout. 

Baer hardly trained for the bout. Braddock, on the other hand, was training hard. "I'm training for a fight, not a boxing contest or a clownin' contest or a dance," he said. "Whether it goes one round or three rounds or ten rounds, it will be a fight and a fight all the way. When you've been through what I've had to face in the last two years, a Max Baer or a Bengal tiger looks like a house pet.