of course, was Zeus, and the two names are actually the same in their linguistic origin, except that Jupiter has the word pater, 'father' (or a form of it) added. Jupiter is thus really 'Zeus pater' or 'Father Sky'.
The apparently unlikely identity of the names (one starting 'Ze-', the other 'Ju-') is acceptable when it is known that in Greek the genitive of Zeus was Dios (compare Latin deus, 'god'), and that the Ju- of Jupiter is related to the Sanskrit dyaus meaning 'sky', 'day', 'heaven'. (Sanskrit as a language has preserved some of the oldest forms of words that are today found in different Indo-European languages.) As for the form Jove, this too derives from a grammatical origin, since in Latin all cases of the nominative noun (name) Jupiter begin Jov (for example, the genitive is Jovis).
All three names so far mentioned (Jupiter, Zeus, Jove) are of course in turn related to that of Diana, which means that we have overall a prestigious and powerful blend of related names and words: Jupiter, Jove, Zeus and Diana all containing a root that means both 'sky', 'god', 'heaven' and 'day'. The original Greek name for the planet Jupiter was Phaëthon, 'shining'.