In Star Trek TOS episode Balance of Terror, Mr. Spock says that Castrodinium is "the hardest substance known to our science." Could it be that it was named after Fidel Castro?
The actual quote is shown below. As you can see, it's not one word ('castrodinium'), it's actually two words ('cast rodinium'), referring to the fictional transuranic element rodinium.
The 'casting' process presumably refers to the method used to make the element into a usable shape.
SPOCK: From the outpost's protective shield. Cast rodinium.
This is the hardest substance known to our science.
(He crushes it with his hand)
The Starfleet Medical Reference Manual offers the following information about the substance but no particular indication of why the name was chosen:
If I had to make a complete guess, I'd say that Roddenberry had decided to name an element after himself.
Even if cast Rodinium was Castrodinium, Cuban dictator (in)Fidel castro was hardly the first or last person to use that surname.
For example, Wikipedia has a long list of persons named Castro:
And of course Rodinium could have been named after someone with the surname Rhodes
I can add rebel general Phillip Roddy to that list
Or other surnames starting with Rhod or Rod.
There is the surname Rodin, - famed French Sculptor Auguste Rodin 1840-1917.
And famous science fiction character Perry Rhodan
And Japanese movie monster Rodan