How did Stalin come to lead the Soviet Union?

Joseph Stalin whose real surname was Dugashviliwas an
early follower of Lenin. He later changed his name to Stalin, meaning "man of steel."
His friends called him "Koba," the name of a Robin Hood type figure who fascinated him
as a child. Although he was paranoid and ruthless, this does not explain his rise to
power. Stalin was also quite cunning. He often sided with members of the politburo
against a single member, thus eliminating that member. Then, he sided with the majority
of the remaining members, thus eliminating those who opposed him one by one. Ultimately,
even Lenin began to distrust Stalin, but Lenin suffered a debilitating stroke. While he
was recuperating, Stalin had special editions of newspapers printed for Lenin's eyes
only which portrayed only good news. Stalin had the phones of other members of the
politburo bugged (including his arch rival Leon Trotsky) and when he learned that
Lenin's will specifically objected to Stalin succeeded him, he intercepted the Will.
Stalin quickly turned on those who had previously supported him, thus securing more
power for himself. Typically, he accused them of being enemies of the Revolution. In
this regard, he was helped by his major henchman, Lavrentia Beria, a psychopathic
murderer. During the Great Purges, Stalin eliminated practically everyone who had
supported him earlier, frequently promising leniency if they confessed, or threatening
their families.  Members of the politburo often slept with pistols under their pillows
to commit suicide should the KGB appear in the middle of the night, so that they might
avoid the hideous torture they knew would await them otherwise. They often held their
breaths when they heard the sound of the apartment elevator, hoping it would not stop on
their particular floor. An excellent but chilling account of Stalin's rise to power and
his stranglehold on the Soviet Union is Simon Begag Montefiore: Stalin, at the
Court of the Red Tsar.