1979 saw the introduction of the Axe bass into Gene's repertoire and the beginning of a life-long association. The basic design of the bass has changed a little through the years and it's been made by several luthiers and companies.
Whether or not this is the first Axe that Gene got or not is something of a mystery. According to Steve Carr his first version of the Axe shown below was made for Gene in 1978 and even used for a few shows that year but no photographic evidence of that exists. According to Gene "the original one was made by Valdez here in Los Angeles, and I still have it around here somewhere". [*] Its first appearance is the photo shoot that was set up the day of the Return of KISS dressrehearsal, 79.06.14. These pics, which found their way into the later versions of the tour book, show the bass with a black blade and black knobs. (My original theory was that the blade was originally silver and refinished black but the dating of the photo shoots are well-established.) The headstock featured Gene's autograph and the pointy shape of the head was mirrored by a bizarre pointed part below the bridge.
[*] 1996 Guitars that Rule the World, Metal Edge presents KISS Alive!

Gene later referenced this bass as being built for the sole purpose of the photo shoot in a video interview for the Japanese music store G-Club.
Perhaps the black blade wasn't quite "axe-like" enough because it was summarily refinished a matte silver by 79.06.20 when the promo videos were shot in Savannah. Looking closely at the pictures the refinished part of the blade is slightly different than the original finish on the edge. Along with the refinish the knobs were changed to match the new color. And for the Valdez Axe that's all she wrote. There are no actual live shots of the bass and after the promo videos it just disappears never to be seen again. If one is to believe the quote from Gene above it may just be locked away in storage since it didn't surface for the auction.
This custom prototype Axe bass was built by Steve Carr who originally came to work for the band when his one-time apprentice became Ace's guitar tech in 1978. "The first project with KISS for me, was when Gene said he wanted a guitar shaped like an executioner's axe. I made several of these until we hit a design that is pretty much what he uses today." [*] The Axe presented here has quite a different design than the one that would end up being used but according to the photos it actually made it on tour with the band, seen here in Knoxville on 79.09.12 next to Spector #2.
[*] 2004 interview at the excellent site www.acefrehleylespaul.com
The string of prototypes that Carr eluded to were probably the ones shown below. The one in the middle does feature the pointy headstock that was a feature of all of the guitars Carr built for KISS (see Ace's mini-Explorer and Paul's Star guitar for instance). The bass on the right is slightly more problematic. On the one hand it has an inlay of Gene's makeup on the headstock that looks very similar to the one that Carr did on Spector #1. On the other hand it was listed in the Butterfields auction without the name of the luthier and it was suggested that it dated from the 1983 Creatures tour (which there is no evidence for, the Axe used on that tour was a Kramer). It has also been suggested that this one is actually from 1981 but that would make it later than the production model Kramer Axe which would cast some doubt on Carr's statement above.
The Kramer Axe was a collaboration between Gene and Kramer of a supposedly limited edition run of 1,000 instruments. By Kramer's own estimations the total only reached approx. 500 before the venture folded after only a year. With an Axe blade similar to both the Valdez and the third "Carr" prototype, this had the appearance of the Axe we've come to associate with Gene. The neck was made of aluminum and featured an easily identified split headstock and wood inlays along the back of the neck for playing comfort. Gene's first Kramer Axe was the 24-fret version with dual humbuckers shown below. To my knowledge it was only used for photo shoots and the Pop Rock performance.
The Kramer Axe that actually saw some real action was a 20-fret version and seems to start its life with cream P-bass pickups (and Gene's favored Quan Badass bridge) for some 1980 photo shoots. However, the pickup covers are quickly changed to black for the Bravo photo shoot and this version shows up backstage in Rome 80.08.29, albeit with new knobs, and is later used in the promo video for Shandi. (Note in the clip that Gene is kind enough to show the wood inlays on the back of the neck.)
By the time the band hits Australia the pickups are switched for Gene's go-to humbucker (again, I'll assume that it is a DiMarzio). The footage from Syndey 80.11.22 and the "video" show the "late 1980" version of the bass in action.
In a rare period of stability the Kramer Axe then actually retains this look throughout the Elder era. Below are pics from the TV performance in Mexico, the video shoot for A World Without Heroes and I, and lastly the sattelite performance for the San Remo festival. Interesting to note is that it was eschewed in favor of the second Spector for the live performance on Fridays which perhaps suggests something about the relative sonic qualities of those two.
Sadly, Steve Carr passed away in 2006 which probably means that this part of the Axe story will forever be shrouded in mystery.
The assumption that this is one instrument that is later modified is based on the fact that it has the Badass bridge which is mounted further back than the production model Axes that are available in collector circles today. Also, the fact that the change is gradual, first the pickup covers then the knobs, also point to this. However...
The date for the video shoot comes courtsey of KISS Alive Forever (p. 117) although it only specifies "Halloween weekend".
In 1982 Gene found active EMG pickups which were summarily installed on all his working basses. The 20-fret Kramer was no exception and for whatever reason the pickup was also moved closer to the bridge. Here comes the true smoking gun that this has been the same instrument all along; in true "working man"-style the previous location of the DiMarzio pickup is simply covered by something that, again, appears to be tape (the picture on the far right). Trying to pin-point the pickup switch is a little difficult: on page 5 of the 10th Anniversary Tour book we see the Axe with it's "old" DiMarzio pickup (along with some hilariously dated pictures) in a promo shoot featuring Ace, but turn the page to page 6 and, lo and behold!, there is Gene with the newly installed EMG. The new look is "officially" introduced for the CON press conference/photo shoot/video taping on 82.10.28. First "live" showing of this version is for the Top Pop taping on 82.11.26. Additionally, a bridge cover was installed over the Badass bridge in classic Gene fashion.
Again, this is an educated guess, but the moving of the pickup could be to fit the additional electronics needed for the active pickup.
This last version of the Kramer Axe carries the load throughout the 10th Anniversary tour making its last known appearance during the South American shows (it can be seen in both the Rio and Sao Paolo footage). So far I haven't seen any real reason as to why Gene moved away from the Kramer to the Jackson below. The design of the blade is the same and the number of frets seem to match. Some players have complained about the aluminum neck of the Kramers which, although extremely stable, can be a bit cold to the touch in the places where the aluminum is exposed. One could also make a case that the position of the pickup had something to do with it but this is all guesswork.
The shift to the Jackson comes about just before the European leg of the Lick it up tour. It's not shown in the tour book photos shot at SIR studios but instead makes its "proper" debut in the video for All Hell's Breaking Loose and can be seen briefly in the footage from Madrid 83.10.14. (And once the American tour book is printed there is a shot of the new Axe for good measure.)

The Jackson Axe continued the new infatuation with EMG pickups, this one located closer to the neck than it had been on the Kramer. The headstock was the standard Jackson "hockey stick" with all four tuners on one side. The headstock and the space between the neck and the bridge had tortoise shell overlays and the bridge was once again hidden from view by a bridge cover.

One curious detail is that the picture from London 83.10.23 appears to show strips of tape making up the black parts of the Axe body. It's harder to see in other photos (none I've found show it quite as well as this one but the one to the left is also decent) but thankfully there is a horrible closeup of Gene's tounge from the 1984 Tourbook (far right below) that shows a detail of the Jackson Axe and the tape on the body. This implies that the taped-up part was probably finished silver originally.
Check I love it loud and I still love you from Madrid to catch a few glimpses of the Axe.
The Jackson Axe is mercifully kept in this near-original condition for at least the two following tours; there are no noticeable alterations. The most high-profile appearance during 1984-1986 is in Animalize Live Uncensored where it gets taken for a spin for Gene's solo spot.

Photos showing the Axe during the Asylum tour, where it did look a bit out of place against the exploding layers of sequined fabric and garish make-up, are a bit lacking but thankfully there is video evidence.
Then things get complicated...
In 1987 Gene turns up with what looks like a slightly altered version of the Jackson. There's a high-gloss, mirror-like finish on the body and headstock, added rivules on the body near the pickup, and, true to form, a hole where there should be (or had been) a tone knob. Apart from those changes it appears identical to the Jackson right down to the black tuning pegs. But, during the Convention Tour of 1995 this bass was part of the museum and was labeled as a prototype Gene Simmons Axe (see pic and video below). The very obvious absence of an Axe during 1990-95, with the possible exception below, might suggest that Gene was in fact trying out various prototypes in preparation of going into the Axe business for himself. Or maybe the rather strange decision to use the Axe for a song like Reason to live during the Crazy Nights tour drove home the point that the Axe was a somewhat odd fit for the image at the time. Whatever the reason for the lack of an Axe, this particular Axe makes its last appearance during the European leg of the Crazy Nights tour, shows up for the convention and then disappears; it doesn't even feature in the auction (which a lot of other Axes do).
Overall there were some factual errors regarding the instruments during the Convention and the tour book was laughably incorrect. It showed a mirror image of the #1 Spector and erroneously dubbed it a "Spectre" bass, even claiming it was the first "Spectre" ever made. The caption next to this Axe bass noted that it was a limited-edition built by Kramer.
...in Makeup to Breakup (p. 199) Peter claims that he got the bass in the Shandi video after they wrapped shooting so perhaps Gene had a couple.
If Gene tried to use the Carr Axe live it probably turned out to be too heavy for use. One of the Viewmaster pics show the thickness of the body to be almost double that of a regular bass.
I think it's fair to say that Gene's techs have made quite imaginative use of simple black tape throughout the years. It also speaks volumes of Gene's "working-bass" concept: as long as it works and looks good enough, it will do.
Collectors take note - unless a Kramer Axe has a Gene Simmons signature that is sealed under the Diamond Coat clear laquer it's not legit.

Interesting fact about the Axe bass, and guitar, from Kramer is that the inlays were actually aluminim dots.
The merchandise form that accompanied the original release of Unmasked showed the Kramer Axe and tells fans to be on the lookout for it in stores in the summer!!