Short answers, pulled from the story.
The Übermensch is a concept Nietzsche introduced in his 1883 book Thus Spoke Zarathustra as a goal for humanity to set for itself. It represents a human ideal grounded in this world rather than in otherworldly Christian values, and it is associated with the creation of new, life-affirming values after the death of God.
Thomas Common translated Übermensch as "Superman" in 1909, following George Bernard Shaw's use of the term in his 1903 play Man and Superman. Walter Kaufmann, writing in the 1950s, criticized this translation and preferred "overman." Some scholars use "superior humans" or simply keep the German word.
A racial interpretation of the Übermensch became a philosophical foundation for Nazi ideas, but this version differs greatly from Nietzsche's original concept. Neither Hitler nor Nazi propaganda used the term Übermensch explicitly, and Nietzsche himself was critical of antisemitism and German nationalism. His sister Elisabeth Förster-Nietzsche, whose husband Bernhard Förster co-founded the Deutscher Volksverein in 1881, manipulated Nietzsche's writings to fit a nationalist worldview.
Zarathustra presents the Übermensch as a goal of self-mastery and the creation of new values, and contrasts it with the "last man," who represents egalitarian modernity and the smothering of aspiration. The "last man" appears only in Thus Spoke Zarathustra and is described as the antithesis of the Übermensch's striving spirit.
Anarchist thinkers were drawn to Nietzsche's hatred of the state, his anti-Christianity, and his call for a transvaluation of values. Emma Goldman defended Nietzsche in her Anarchism and Other Essays, and Murray Bookchin described the workers' reconstruction of society as a Nietzschean project in his 1973 introduction to The Anarchist Collectives.
In Ecce Homo, Nietzsche described the Übermensch as designating a type of supreme achievement, as opposed to modern men, good men, Christians, and nihilists. He wrote that those seeking the Übermensch would be better off looking for a Cesare Borgia than a Parsifal, pointing to the Italian Renaissance as an embodiment of the concept.