(Knut) Otto (Reinhold) Löwenborg (Loewenborg, Loevenborg, Løwenborg, Løvenborg) (2 March 1888 – December 1969) was a Swedish chess master.
In January 1912, he won a simultaneous exhibition game against Frank James Marshall in Stockholm.[1] He took 3rd at Stockholm 1913 (Boris Kostić won), took 9th at Jungbunzlau (Mladá Boleslav) 1913 (Karel Opočenský won),[2] tied for 2nd–4th at Copenhagen 1916 (the 9th Nordic Championship, Paul Johner won),[3] took 8th at Stockholm 1916, took 6th at Kristiania 1917 (the 10th Nordic-ch, Gustaf Nyholm won), shared 1st with Anton Olson and won a match against him (3–2) at Stockholm 1917, and finally lost a match for the Swedish Champion title to Nyholm (1–4) at Stockholm 1917.[4]
He tied for 7–8th at Göteborg 1918 (Karl Berndtsson won), tied for 4–6th at Göteborg 1919 (the 11th Nordic-ch, Rudolf Spielmann and Olson won), and tied for 4–8th at Copenhagen 1924 (the 12th Nordic-ch, Aron Nimzowitsch won).[5]