I stumbled upon this flash fiction contest for stories of 250 words or less, with the theme, troubled or troubling supermen, conducted by Hilobrow.com. Their contest is interesting, but I found their explanation of the theme, pre-golden-age supermen, or "Radium Age" fiction, as author Joshua Glenn called it, quite entertaining. Here is the contest theme:

Long before Alan Moore asked “Who will watch the Watchmen?” Radium-Age (1904-33) science fiction writers worried whether supermen would rescue us ordinary mortals — or try to dominate us.

The link in the quote above is to an earlier io9 article, which was the source of some of the Hilobrow article on pre-golden-age science fiction. The author provides ten SF novels published in the 1904-1933 period as examples, including some nicely retro book covers, including Poul Anderson's Brain Wave.

The Radium Age superman was superior in body and intellect, along several evolution-inspired lines of reasoning, including "greater capacity for action and freedom."

Aye, there’s the rub: for, as Nietzsche has Zarathustra predict, “Just as the ape to man is a laughingstock or a painful embarrassment, man shall be just that to [superman].”

Included in the article is a summary of the ten most influential novels of the Radium Age, with a synopsis of each, and the cover art. There is also a bibliography of related fiction from the period 1804 to 1937, under several sub-genre categories.