The SS-Totenkopfverbände (SS-TV) — the Death's Head Formations — were made up of Nazi Germany's concentration camp guards. During World War II the SS-TV also provided troops for the first combat unit of the Waffen-SS, the Totenkopf Division, which eventually evolved into one of Nazi Germany's most formidable combat formations.

The SS-TV was established by Standartenführer Theodor Eicke to provide the personnel for the manning of the concentration camps, such as Dachau (where the first unit was established), Sachsenhausen and Oranienburg, the town north of Berlin where the Eicke's office had been established.

Following the Night of the Long Knives, a purge ordered by Adolf Hitler of potential political rivals in the Sturmabteilung, or S.A. in June 1934, Eicke, who had played a major role in that affair, was appointed the Inspector of Concentration Camps and Commander of SS guard formations (Inspekteur der Konzentrationslager und Führer der SS Wachverbände); he was also promoted to the rank of SS-Gruppenführer. On March 29, 1936, the Reichsführer SS officially designated these units as the SS-Totenkopfverbände. The term Totenkopf, or “Death's Head,” remained until the dissolution of the SS in 1945, although the nature of the organization had changed dramatically before and during the war.

Sources: Wikipedia

The SS (Schutzstaffel): Totenkopfverbände (Death's Head Formations)