Science fiction has sometimes been accused of having few memorable characters. John C. Wright does a survey, based on his own list of 50 essential science fiction authors. My favorite observation, simply because it’s so true:

Heinlein’s protagonists tend all to be the single archetypal Heinlein character: the eager young boy who grows into a wry but all-competent jack-of-all-trades and eventually into a wry and crusty old man, usually marrying a lusty jill-of-all-trades nudist redhead somewhere along the way. Asimov’s protagonists are much the same, but with less wryness and no redhead. Van Vogt’s protagonists are much the same, but with no wryness at all, sometimes with amnesia, and he evolves into a superhuman rather than a crusty old man.

Not surprisingly, characterization has improved over the years.