This video. It's also the video that introduced me to Dino, and eventually Fear Factory.
Oh, and as silly as it sounds, Brad Delson of Linkin Park. When I saw him use those RG7620's in some early live Linkin Park videos, I immediately thought "Do want."
I was inspired to move to 7's after hearing the how vastly different a 7 sounds than a 6 from a tone perspective. It's something that drew me in and grabbed ahold of my ear drum and wouldn't let go.
After moving to 7's, I actually went back to 6's for awhile. Late last year I had another "moment" and said time to get back to the 7. I dumped all but 2 of my 6's. I now have 3 7's and 1 8 string. I'm not going back this time!
Bands like Vildhjarta have really captured my imagination as of late.
I kind of discovered JP, Vai, and Rob Johnson all around the same time in 96 and got Meshuggah's D.E.I. around then too. But I finally got pushed over the edge and bought one after getting Dead Heart in a Dead World, but I'd mainly cite JP.
I was looking at buying my first decent guitar and found a pretty decent deal on a seven. I thought "Why not? It'll give me access to more tunings without too much dicking about"
Korn and Dino Cazeras made me aware of their existence. Then I discovered John Petrucci, Jeff Loomis, and Chris Broderick all around late 90's/early 00's (Metropolis Pt. 2, Dreaming Neon Black, and Thane to the Throne specifically the albums that got me into them), and kinda sealed the deal on me wanting a 7.
Meshuggah, Korn, Nevermore, Chris Broderick, Cannibal Corpse, Dino Cazeras, Whitechapel, Dream Theater. All of those pretty much made me want to experiment with 7 strings\extended range guitars.
If i had to pick a single guitarist, I guess itd be John Petrucci. "A Change of Seasons" changed the way I thought about ERGs. No longer did I just view them as a means to CHUGGAH lower, but create something more musical with added range. For me, it was moreso the fact that I like going against the norm, and wanted something different to help inspire new writing. The thoughts of having full upper range for leads while having 5-7 semitones lower than standard E for chording/riffing seemed like a very intriguing concept.
Funny side story: as I was tinkering with the 7321 in the store that I later bought that day, the sales guy brought me over a 2228 and said "here try this out". At the time my thought was "wow this thing is overkill...ill never need or want an 8 string, its just too much..." And 3-4 short years later, guess who's GASing ridiculously hard for an 8...
my biggest influence is -of course- John Petrucci 1st I heard Dream Theater's The Glass Prison, that song was brutal -and still brutal till now - then I go back to Awake album n so on.. I also Listened to Steve Vai, Dino Cazares, Trivium's Matt Heafy, n then I found that Joe Satriani also played a 7 strings..
Steve Vai was a great influence definitely, but Emperor's "Prometheus: The Discipline of Fire and Demise" was a great revelation to me... He used his 7 string so melodically imho instead of that breakdownish sound so often used with tuned down guitars...