Gregor Strasser (1892-1934) was an early rival of Adolf Hitler's for the leadership of the Nazi party. He was murdered in the Night of the Long Knives.
Like Hitler, he had served in World War I and received the Iron Cross for bravery. Together, they participated in the Beer Hall Putsch, an attempt by the nascent Nazi party to overthrow the government of Bavaria in 1923. Along with other participants, both men were thrown in jail for a few years afterwards.
After being released, Strasser moved to north Germany and became a leader of the Sturm Abteilung (SA). He developed a large following and became leader of the revolutionary wing of the Nazi party.
Unlike Hitler, Strasser was a socialist. He reached a very senior position in the party, becoming Reichsorganisationsleiter (Organisational Leader of the Reich). He was even offered the Chancellorship of Germany in 1932, before Hitler was, but declined it and also resigned from all his formal party assignments at the same time. Perhaps he already sensed just how dangerous Hitler was going to be to his perceived rivals.
Strasser was apparently a full supporter of Hitler's racist views, but differed on all economic matters. Certainly, you can't imagine Hitler writing the following:
We are Socialists, enemies, mortal enemies of the present capitalist economic system with its exploitation of the economically weak, with its injustice in wages, with its immoral evaluation of individuals according to wealth and money instead of responsibility and achievement, and we are determined under all circumstances to abolish this system ! And with my inclination to practical action it seems obvious to me that we have to put a better, more just, more moral system in its place, one which, as it were, has arms and legs and better arms and legs than the present one !
Professionally, Strasser was a pharmacist, and he returned to that work when he backed away from his party positions. He had also published magazines with his brother Otto. This lead to conflict with Joseph Göbbels, who demanded control of all publications in Berlin. Göbbels retaliated in part by spreading the story that Strasser's mother had been Jewish.
A tidbit -- Strasser used to brag that he knew two great secrets about Hitler: the origins of the man's venereal disease, and the true story of what had happened to Hitler's niece and lover, Geli Raubal. If so, his secrets died with him.
Sources:
"Mysteries of WWII vol.1"
http://www.spartacus.schoolnet.co.uk/GERstrasser.htm
Gregor Strasser, Thoughts about the Tasks of the Future. 1926
http://www.portal-ns.com/thecensure/mem4.htm