Short answers, pulled from the story.
The Hitler Youth traces its origins to 1922, when the Munich-based Nazi Party established its official youth wing, the Jugendbund der NSDAP, announced on the 8th of March 1922. It was officially renamed Hitler-Jugend, Bund deutscher Arbeiterjugend on the 4th of July 1926, a name taken up on the suggestion of Hans Severus Ziegler.
By 1940, the Hitler Youth had eight million members. Membership had grown from around 25,000 boys in 1930 to over five million by December 1936, with the sharpest single-year jump occurring in 1933, when membership reached 2,300,000 after the Nazis came to power.
Membership became legally mandatory for Aryan youth in December 1936 under the Gesetz über die Hitlerjugend. This obligation was reaffirmed in March 1939 by the Jugenddienstpflicht, which conscripted all German youths even if their parents objected, with non-compliant parents subject to investigation by the authorities.
Artur Axmann, who became Reichsjugendführer on the 8th of August 1940, converted the Hitler Youth into an auxiliary military force. In 1944, the 12th SS-Panzer-Division Hitlerjugend, made up of members born in 1926, fought in the Battle of Normandy; over 20,000 youths participated and 3,000 were killed. By 1945, the Volkssturm was drafting Hitler Youth members as young as twelve.
The two men who held the rank of Reichsjugendführer were Baldur von Schirach, who was appointed in 1933 and held the position until 1940, and Artur Axmann, who succeeded him on the 8th of August 1940 and led the organization until the end of the war.
Baldur von Schirach was sentenced to 20 years in prison, though for crimes against humanity as Gauleiter of Vienna rather than for leading the Hitler Youth. Artur Axmann received a 39-month prison sentence in May 1949 and was not found guilty of war crimes; a West Berlin court later fined him 35,000 marks in 1958 for indoctrinating German youth with National Socialism.