"could be under the umbrella of Sci-Fi. "

I see he's not included in the list in Wikipedia.

Like 'folk', some umbrellas are a bit large to suit me. ;>)

Categories are always pretty subjective... I like lots of sub-categories in order to clarify...even if just to myself... what I refer to.

(I did learn from that list that even good ol' Theodore Sturgeon was a pen name.)