ceebeegee | A thing that makes me go hmmm...

So I'm reading the wikipedia entry about the '70s TV show, Shazam!, all about Captain Marvel, the World's Mightiest Mortal. My brother Bart and I used to watch this show when we were kids--I remember asking my dad what a mortal was, and liking that Captain Marvel's altar ego, Billy Batson, had such an alliterative name. (This was around the time I was learning to read, or had just learned, and I remember really responding to the sound of things. Living in South Florida, we would see I-95 signs everywhere, and I would chew over the assonance of those signs. Eye...nine...five.... I suppose it's no surprise I ended up loving poetry.) Here's the question--SHAZAM (the word Billy says to invoke the power of the gods to transform into Captain Marvel) stands for Solomon, Hercules, Atlas, Zeus, Achilles, Mercury. Why are some of the names in their Greek forms (Zeus instead of Jupiter) and some in their Roman forms (Hercules instead of Heracles, Mercury instead of Hermes)?