Totenkopf is the German word for "Death's Head" and is used to describe a military insignia featuring a skull with crossed bones. 

The symbol and its name are sometimes associated with Nazi Germany, particularly the SS and Waffen-SS. However, the use of the symbol as a military insignia began with the cavalry of the Prussian army under Frederick the Great. In Russia, the use of this symbol can be traced even further back: during the Tatar occupation, Christian Orthodox warrior monks going to battle used to wear this symbol (called "Adam's Head"). 

Frederick formed Husaren-Regiment Nr.5 (von Ruesch), a Hussar regiment commanded by Colonel von Ruesch. These Hussars adopted a black uniform with a Totenkopf emblazoned on the front of their Mirletons and wore it on the field in the War of Austrian Succession and in the Seven Years' War. 

Hussar from Husaren-Regiment Nr.5 (von Ruesch) in 1744 with the Totenkopf on the MirletonIn 1808, when the regiment was reformed into Leib-Husaren Regiments Nr.1 and Nr.2, the Totenkopf remained a part of the uniform. 

Prussia was not the only nation to use the Totenkopf. The Kingdom of Sweden's Hussar Regiments wore it in the Prussian Style on the front of the Mirleton. The Russian Kornilov regiment adopted it in 1917. 

During the Napoleonic Wars, when Frederick Duke of Brunswick-Luneburg was killed in battle, his troops changed the colour of their uniforms to black, with a Totenkopf on their Shakos in mourning their dead leader (Other sources claim that the "Black Brunswickers" were so equipped while Friedrich Wilhelm of Brunswick lived, as a sign of revenge on the French [1]). The deaths head continued to be used throughout the Prussian and Brunswick Armed forces until 1918. 

The Totenkopf was used throughout the inter-war period, most prominently by the Freikorps. In 1933 it was in use by the regimental staff and the 1st, 5th, and 11th squadrons of the Reichswehr's 5th Cavalry Regiment. 

In the early days of the NSDAP, Julius Schreck, the leader of the Stabswache (Adolf Hitler's bodyguard unit), adopted the Totenkopf for his unit. In 1935, the Stabswache was renamed as the Schutzstaffel (SS) and the SS continued to use the Totenkopf as insignia throughout their brief history. As they had done with the Swastika, the Nazis simply adopted the Totenkopf from the historical tradition and used it for their own purposes, leaving it marked with a stigma that has continued to the present. 

Regimental cap badge of the Queen's Royal LancersThe skull with crossed bones is also the current insignia of a regiment in the British Army, the Queen's Royal Lancers. The badge has been used by the Lancers since 1859 and is a reference to the participation of the 17th Lancers in the Charge of the Light Brigade at the Battle of Balaclava.