Krav Maga began with a single man - Imrich Lichtenfeld, who later took the name Imi Sde-Or. Born in 1910 in Budapest, he grew up in Bratislava, the capital of Slovakia, in a home where sports, law, and Central European education were equally respected. Samuel Lichtenfeld, Imi's father, was a unique figure. At the age of thirteen, he joined a traveling circus, and for the next twenty years engaged in wrestling, weightlifting, and various demonstrations of strength. For him, the circus was also a school in which he met people involved in a wide variety of sports. These people taught Samuel what they knew - including various martial arts.

With his father's encouragement, Imi became active in a wide range of sports. He first excelled in swimming, then in gymnastics, wrestling, and boxing. In 1928, Imi won the Slovakian Youth Wrestling Championship, and in 1929, the adult championship (in the light- and middle-weight division). That year, he also won the national boxing championship and an international gymnastics championship. During the 1930s, Imi's athletic activities focused mainly on wrestling, both as a contestant and trainer.

In the mid-thirties, conditions began to change in Bratislava. Fascist and anti-Semitic groups appered, determined to upset the public order and harm the city's Jewish community. Imi became the un-crowned leader of a group of young Jews, most of them with a background in boxing, wrestling, and weightlifting. This group attempted to block the anti-Semitic bands from entering the Jewish quarter and wreaking havoc. In 1940, having become a thorn in the side of the anti-Semitic local authorities as a result of his activities, Imi left his home, family, and friends and boarded the last immigrant ship that succeeded in escaping the Nazis ' clutches. The vessel was an old riverboat named Pentcho that had been retrofitted to carry hundreds of refugees from Central Europe to the land of Israel (then called Palestine).