Christian IX (8 April 1818 –29 January 1906) was King of Denmark from 1863 to 1906. From 1863 to 1864, he was concurrently Duke of Schleswig, Holstein and Lauenburg.

Growing up as a prince of Schleswig-Holstein-Sonderburg-Glücksburg, a junior branch of the House of Oldenburg which had ruled Denmark since 1448, Christian was originally not in the immediate line of succession to the Danish throne. However, in 1852, Christian was chosen as heir to the Danish monarchy in light of the expected extinction of the senior line of the House of Oldenburg. Upon the death of King Frederick VII of Denmark in 1863, Christian acceded to the throne as the first Danish monarch of the House of Glücksburg.