Star Trek

Was it taken from the god or the planet?

I'm not entirely certain what you mean. Are you wondering if the Star Trek creators named the planet Vulcan after the god?

I think the god Vulcan existed long before the planet Vulcan was created in the show.

I probably didn't make myself too clear. I'm asking what Gene Roddenberry, and his assistants I imagine, based the name Vulcan on--the Roman god or the once-hypothesized planet between Mercury n the Sun.

Ok, now I understand. I'm not really sure. I've always assumed the Roman god, but I don't know for certain.

As most of the planets are named after ancient gods, because they were thought to actually be the gods, I believe the safe answer to your question is "both".

In Roman mythology Vulcan was the god of fire, and was said to have made Pandora, the first of mortal women.    He was also the counterpart of  Hephaestus.  It was also said to be the name of  a hypothetical planet nearest the sun whose existence was erroneously postulated to account for perturbations in Mercury's orbit.

Whcih one was Roddenvery inspiration, probably he knows ....

http://www.angelfire.com/mythologywonderland/hephaestus.html

It was said that originally, Spock was supposed to have red skin, and that he came from a desert plaent that was extremely hot; therefore, Vulcan. The change in skin color came after tests that showed that red did not show up in black and white; so then they switched to green, which caused histeria in the color correction department - they recolored him to the norm, screwing up all the makeup that Freddid - so they toned it down, with just green/purple highlights on his cheeks, lips, and eyes.

So, answer: Vulcan/hot/forge/fire etc. 

 A bit off topic but it is also interesting to note that originally Spock claims that one of his ancestors was human, infering a more distant relation than his mother. This would have made Spock more vulcan than human rather than 50/50.