Himmler grew up to Privelege in Bavaria, and during the 1st World War, had the intention of becoming a professional military officer. However, he was never very athletic, and he struggled during military training. Germany's defeat in World War I squashed his dreams of being a Military Officer, and he found himself at odds with the world around him.
Himmler joined the party in the Early 20s, and took part in the Putsch in 1923, and was loyal to the Party following. In 1925, he became a leader within the Schultzstaffel (SS), and was District Leader for the Bavarian district.
By 1929, Himmler was promoted to Reichsfuhrer-SS (being at that time simply a title for National Commander of the SS, and not to be confused with the Reichsfuhrer title that Hitler held). At the time, the SS had a total of 290 members. Himmler began a major expansion of the organization, and by 1933, the group had grown to 52,000 members.
Himmler was very interested in the Nazi Mythos, and was a founding member of the Ahenerbe. He was later appointed as the National Leader of all police, and saw a further expansion of the SS to numbering close to over a million during the war. He was incredibly loyal to Hitler and the party, until near the end of the war.
Germanization & the Holocaust
Himmler was tasked with carrying out the General Plan for Germanization of the East. This included unsettling large numbers of ethnic poles, and reclaiming ethnic Germans in the area. Those who fought back against the deportation, soon found themselves in Concentration Camps.
Himmler oversaw these too, and new of their atrocities personally. As commander of the SS, his forces rounded up political dissidents, Jews, and other people 'not deserving to live', and interned them. They then forced them into slave labor, did horrific medical experiments on some, and later attempted to exterminate all.
Himmler saw that the war was going to end badly, and attempted to negotiate a surrender to American Forces via Swedish channels. His attempt failed, and by the 28th of April, Hitler learned of this attempt personally. He flew into a rage, and after he calmed down, called it 'the worst act of treachery' he had ever known. That, and given that the Soviets were only 300 meters away, prompted his suicide.
In Hitler's WIll & Testament, Himmler was stripped of all rank and title. Now unwanted by his comrades, and hunted by his enemies, he attempted to disguise himself so that he could return to Bavaria. He shaved his mustache, wore an eyepatch, and falsified his papers. However, one whose papers were so complete marked suspicion for British troops, and he was arrested on May 22nd.
The next day Himmler committed suicide via a cyanide tablet, and shouted 'I am Heinrich Himmler' in the last moments.