German political activist who, with his brother Gregor (Strasser, Gregor), occupied a leading position in the Nazi Party during its formative period. His leftist leanings and opposition to Adolf Hitler (Hitler, Adolf) caused his downfall shortly before Hitler's accession to power.

Strasser was born into a Bavarian middle-class family. After Gregor joined the Nazi Party and was elected to the Reichstag (federal lower house), Otto and Joseph Goebbels (Goebbels, Joseph) joined him in organizing a mass movement around the party in the 1920s. They appealed to the lower middle classes and the proletariat by advocating a socialism couched in nationalist and racist terminology; the Nazi gains at the polls after 1928 were partly due to their efforts. Otto, however, became disillusioned with Hitler when he began to realize that the Nazi Party, as it was evolving under Hitler's leadership, was becoming neither socialist nor a party of the workers. After Hitler began forming alliances with Germany's industrial magnates in return for their financial support, Otto left the party (1930) and organized the Schwarze Front (Black Front); his brother, however, continued to support Hitler.

After Hitler's accession to the chancellorship, both Otto and his brother lost almost all their influence. Gregor was murdered on Hitler's orders during the Röhm purge of 1934, but Otto managed to escape and go into exile. He finally settled in Canada. Returning to Germany in 1955, he failed in an attempt to reenter politics.