Count Carl Johan Magnus Björnstjerna (7 April 1886 – 20 February 1982) was a Swedish officer and horse rider who competed in the 1928 Summer Olympics. He and his horse Kornett won the bronze medal as part of the Swedish jumping team after finishing ninth in the individual jumping.^[1][2]

Björnstjerna was born on 7 April 1886 in Stockholm, Sweden, the son of colonel, count Gustaf Björnstjerna and his wife Ellen Jonzon.^[3]

Björnstjerna became a lieutenant in the Life Regiment Dragoons in 1909 and was promoted to ryttmästare in 1921. He then served as a staff adjutant and captain of the General Staff in 1921 and as ryttmästare and squadron commander in the Life Regiment Dragoons in 1925. Björnstjerna was appointed chief adjutant and major of the General Staff in 1928 and then served as head of the General Staff's Foreign Department from 1930. He was promoted to lieutenant colonel and was posted as military attaché in London, Paris and Brussels from 1933 to 1935. Björnstjerna was promoted to colonel in 1935 and served as commanding officer of Norrland Dragoon Regiment from 1935 to 1940. He transferred to the reserve in 1946.^[3]

Björnstjerna was married 1915–1954 to Sonja Wallenberg (1881–1970), the daughter of Marcus Wallenberg Sr. and Amalia Hagdahl.^[4][3] They had four daughters. In 1956 he married Ulla Nilsson.

• 1909 – Lieutenant
• 1921 – Ryttmästare
• 1928 – Major
• 1933 – Lieutenant colonel
• 1935 – Colonel

Björnstjerna's awards:^[4]