Eicke was born in Solingen on October 17 1892 as the son of a station master. After dropping out of school at the age of 17, he became a member of the 23rd Bavarian infantry regiment in the German army; later on, he took the office of paymaster for the 3rd - and, from 1916 on, the 22nd - Bavarian infantry regiment.
Having won an Iron Cross during World War I for bravery, Eicke nevertheless did not have any prospect to find work after the end of the war; he began studying in his wife's hometown Ilmenau, but dropped out of school again in 1920 to pursue a police career, initially as an informer and later on as a regular policeman.
After failing again, due to not only his lack of a school degree, but also his fervent hatred for the Weimar Republic and his repeated participation in violent political demonstrations which was not allowed to police officials. He finally managed to find work in 1923 at the IG Farben in Ludwigshafen, soon rising to the rank of the leader of the company's internal intelligence service.
Staying politically active, Eicke joined the Nazi party on December 1 1928, and also became a member of Ernst Röhm's SA, which he left again in August 1930 in favour of the SS, where he quickly rised in rank after recruiting new members and building up the SS organization in the Bavarian palatinate, having been promoted to SS-Standartenführer (roughly equivalent to Colonel) by Heinrich Himmler by the end of 1931.
His political activities also caught the attention of his employer, though, and in early 1932, he was laid off by the IG Farben. At the same time, he was caught preparing bomb attacks on political enemies in Bavaria, which he received a two year prison sentence for in July 1932. However, due to protection received from Franz Gürtner, who would later become minister of justice under Adolf Hitler, he was able to escape the sentence and instead fled to Italy on an order from Heinrich Himmler, where he overtook responsibility for a camp for fled SS members.
Eicke then returned to Germany in March 1933 following Hitler's rise to power; after political quarrels with Gauleiter Joseph Bürckel and spending several months in a mental asylum, he was remembered by Himmler in June 1933 and made commander of the Dachau concentration camp on June 28 after complaints and criminal proceedings against former commander Hilmar Wäckerle following the murder of several detainees.
Upon overtaking command of the camp, Eicke immediately began reforms, establishing new guarding provisions, which included blind obedience to orders, and tightening disciplinary and punishment regulations for detainees, which were adopted by all concentration camps of the Third Reich during the following years.
Eicke's radical anti-semitism and anti-bolshevism as well as his insistance on blind and unconditional obedience towards him as the camp's commander as well as the SS and Adolf Hitler made an impression on Himmler; on January 30 1934, he was promoted to SS-Brigadeführer (equivalent to Major-general), and in May 1934, he was appointed "inspector of concentration camps", a position which he began working in on July 4 1934. Although technically responsible to the SS-Hauptamt, Eicke in fact reported directly to Heinrich Himmler.
Eicke also was involved in the Night of the Long Knives in summer 1934; together with hand-chosen members of the Dachau concentration camp guards, he helped out Joseph Dietrich's SS-Leibstandarte Adolf Hitlers to imprison SA commanders on June 30, and to show his obedience to Himmler and Hitler, he murdered Ernst Röhm together with his adjutant Michael Lippert on July 1 1934, for which he was promoted again to SS-Gruppenführer.
In his role as the "inspector of concentration camps", Eicke began a large reorganisation of the camps until 1939; this consisted of the dismantling of the smaller camps until August 1937 when only Dachau, Sachsenhausen, Buchenwald and Ravensbrück (near Lichtenburg) remained as well as the building of new camps in Austria (e.g. Mauthausen in 1938) and the reformation of the camps' administrations to follow the Dachau model.
Eicke's reorganizations and the introduction of forced labour made the camps one of the SS's most powerful tools; this earned him the enmity of (among others) Reinhard Heydrich, who had already unsuccessfully attempted to take control of Dachau in his position as commander of the Bavarian political police. Eicke, with support from Himmler, prevailed, though, asserting that the command structure he had introduced would not only stay until 1945, but also not be responsible to the Gestapo and SD when the office of the inspector of concentration camps was turned into the Amt D of the Wirtschafts- und Verwaltungshauptamt under Oswald Pohl in 1940.
It was this and other things that earned Eicke a fearsome reputation even within the SS; he was described as brutal and evil, distrustful, cruel and plagued by his exuberant ambitions, full of hatred for everyone who did not agree with the Nazi ideology.
Eicke's attitude of "inflexible harshness" also influenced the guards in the concentration camps; constant indoctrination removed any compassion for the detainees from the guards and created an atmosphere of controlled, disciplined cruelty that lived on even when Eicke was not involved with the concentration camps anymore. Among those who were influenced by Eicke this way were Rudolf Höß, Franz Ziereis, Karl Otto Koch and Max Kögel.
Eicke's drill also contributed to the establishment of the SS-Totenkopfverbände ("SS Death's Head Units") which were part of the Waffen-SS and many members of which were former concentration camp guards, and in fact, creating these units was one of Eicke's main tasks between 1936 and 1939. Later, after the beginning of World War II, Eicke became commander of the Totenkopf-regiments "Upper Bavaria", "Brandenburg" and "Thuringia" in Poland, carrying out the "special task" of killing perceived enemies like jews, former government officials and "rebels" in the areas behind the 8th and 10th army. These tasks then led to Hitler approving Himmler's recommendation to form three SS-divisions in October 1939, among them the notorious 3rd SS-division Totenkopf ("death's head") under the command of Theodor Eicke.
During the course of the war, Eicke and his division distinguished themselves by an unmatched brutality and several war crimes, including the murder of British POWss in Le Paradis in 1940, the murder of Russian commissioners and the plundering and pillaging of several Russian villages.
The Totenkopfdivision, who called their commander "Daddy Eicke", continued to show an unmatched fanatism and stubbornness; both during the advance in 1941 as well as the summer offensive in 1942, the conquest of Charkov, the so-called cauldron of Demjansk and the defending of Warsaw and Budapest in 1944 / 1945, they fought with unrivaled cruelty and never cared about their own losses. The Totenkopfdivision has thus been described as the logical continuation of Eicke and his own brutal methods.
Theodor Eicke himself died on February 26 1943; shortly after being promoted to SS-Obergruppenführer (equivalent to full general) in 1942, his plane was shot down by Russian infantry near Orella during Operation Barbarossa, an end which was glorified as a "hero's death" in German propaganda.