What follows assumes you know that BATTLE FEVER J (the third sentai series, and the one which kicked off the current cycle of shows in 1979) began life as a collaboration between Toei and Marvel Comics. The original idea between BFJ was along the lines of "Captain Japan," and evolved into something resembling the Avengers before it mutated into its current form. That's where our story picks up...
Here’s a fun fact about super sentai: In addition to BATTLE FEVER J, both DENZIMAN and SUN VULCAN were also considered collaborations between Toei and Marvel Comics Group. I don’t know how much actual involvement Marvel had with DENIZMAN and SUN VULCAN, but you can still find old merchandise that includes “MCG” alongside Toei and TV Asahi in the copyright information. The Marvel connection was dropped after SUN VULCAN, and subsequent sentai series don’t include it. In fact, it appears to have been retroactively eliminated from DENZIMAN and SUN VULCAN.
Another fun fact: Yukie Kagawa (“Amazoness” in Toei’s SPIDERMAN series) played “Amazon Killer” in SUN VULCAN. As you might gather, the two roles were somewhat similar.
Here's the Japanese Wikipedia page for Marvel Comics, and here's the (imperfect) Google translation.
To see the original entry that prompted this, click here.