Gerhard Roßbach (28 February 1893 – 30 August 1967), also spelled Rossbach, was a German Freikorps leader and nationalist political activist during the interwar period. Born in Kehrberg, Pomerania, he gained prominence for his involvement in various right-wing paramilitary groups following World War I and in particular for his close association with Ernst Röhm, who served as an important intermediary in the early 1920s between those right-wing paramilitary organizations and upper echelons of the Reichswehr. Rossbach is generally credited with inventing the brown uniforms of the Nazi Party after supplying surplus tropical khaki shirts to early troops of the Sturmabteilung (SA).

Waite, who produced the early historical standard study of the Freikorps movement, writes (ironically) of Roßbach that, "The true Landsknechte ['Freebooter'] type which the National Socialists were later to extol as the possessor of 'the moral strength of the race,' is personified in Gerhard Roßbach the notorious Free Corps leader who became the first adjutant of Hitler's S.A."

In his biography of Adolf Hitler, Heiden transcribed Roßbach's recollection of his early days as a Freikorps commander:

"It was the beautiful old Freebooter class of war and post-war times .. organizing masses and losing them just as quickly, tossed this way and that way just for the sake of our daily bread; gathering men about us and playing soldiers with them; brawling and drinking, roaring and smashing windows — destroying and shattering what needs to be destroyed. Ruthless and inexorably hard. The abscess on the sick body of the nation must be cut open and squeezed until the clear red blood flows. And it must be left to flow for a good long time till the body is purified."

Having enlisted in the infantry prior to the outbreak of the First World War, Roßbach fought on the Eastern Front as a member of the 175th (8th Prussian) Infantry under XVII Corps in the 8th, 9th, and finally under the 7th army of the Imperial German force. This unit moved around quite a bit, which is symptomatic—in the record-keeping system characteristic of Imperial German command—of very heavy casualties being intentionally concealed to maintain morale or otherwise getting lost in their documentation as the war unfolded. In addition to the many battles in which they participated, Roßbach's army group bore responsibility for the defense of Silesia and the Danzig area for significant periods of the war.

Like many officers who fought for most of the war in the East, Roßbach was finally called to the Western Front, where he was seriously wounded in either the Battle of Lys, part of Ypres, or in the second battle of the Marne). He was thereafter promoted to First Lieutenant.

Roßbach's Freikorps activities, particularly in the Silesian Uprisings, had a marked continuity with his service as infantry officer during the First World War, with the important difference that all of these activities were illegal under the terms of the Treaty of Versailles and the law of the Weimar Republic. During the Baltic fighting of 1919, his Freikorps Roßbach made an extremely long march from Berlin across Eastern Europe to rescue the Eiserne Division (another Freikorps) from destruction by the Latvian Army.

Waite writes that, "Whatever one thinks of the man's character, [Roßbach's]...rescue of the Iron Division must remain one of the great feats of military history. Braving an early and unusually harsh Baltic winter, Rossbach led his badly equipped men over a twelve thousand mile trek from Berlin across Eastern Europe. They often marched forty miles a day. As soon as they arrived at Thorensberg, the Rossbach Detachment attacked the Latvian army, cut a path through to the beleagured Iron Division, and held off the Latvians until Bischoff's men could escape."