Sir Horace George Montagu Rumbold, 9th Baronet, GCB, GCMG, KCVO, PC (5 February 1869 – 24 May 1941) was a British diplomat.

A well-travelled man who learned Arabic, Japanese and German, he is largely remembered for his role as British Ambassador to Berlin from 1928 to 1933 in which he warned of the ambitions of Hitler and Nazi Germany.

Rumbold was in charge of the British Embassy when the ambassador, Sir Edward Goschen, went home on leave on 1 July.

[3] After the war, he was appointed ambassador to Poland in 1919,[4] The following year, he became the High Commissioner to Constantinople during which he signed the Lausanne Treaty on behalf of the British Empire.

[6]Rumbold concluded by giving stark warnings for the future of international relations: ...it would be misleading to base any hopes on a return to sanity...[the German government is encouraging an attitude of mind]...which can only end in one way....

[8] Ralph Wigram, an official in the Foreign Office, gave Winston Churchill a copy of this despatch in the middle of March 1936.

[10] Walter Laqueur concurred by claiming that Rumbold's "prophetic" insights explained the Third Reich better than the expert opinions that were later issued from the OSS.