Which bands/artists opened the prog portal?

Rush did it!

Originally posted by zoviet there will surely be that 1 or 2 bands or albums that dragged you kicking and screaming into the blackhole that is prog! I', gonna name 2 of my fav bands ever whom because of my obsession with their awesomeness got me hooked onto prog like a sick junkie whore, always craving more more related yet adventurous sounds, and what i was led to hahaha:   TORTOISE - Can, Neu, Faust, krautrock - Yes, Camel - This Heat - Shadowfax and new age fusion, worldbeat - Spyro Gyra, Yellowjackets, smooth jazz fusion - Bitches Brew, In a silent way   SUPERSILENT - King Crimson, especially the dbl trio incarnation and Projeckts - rest of electric Miles catalogue - ECM, Terje rypdal - Tangerine Dream - New age synth - classic 70s jazz fusion

No doubts it was Pink Floyd:

Dream Theater

For me, it was watching the Asia in Asia concert live on MTV. They gave a little background on where each member had come from. Palmer just blew me away! I ran out the next day and bought ELP's "Welcome Back My Friends..." Album and I have been hooked on Prog ever since.

Thanks to my father's collection, I get used to listen to Pink Floyd, Mike Oldfield, Pat Metheny and Jean-Luc Ponty at an early age.
Then, he began bringing records of Rick Wakeman, Yes and Jethro Tull from the library.
So, I was exposed to the first wave of Progressive Rock in its purest form at a quite young age.

Frank Zappa.

I was kind of bombarded from different sides. First there was Pink Floyd, I got The Wall and Delicate Sound of Thunder, and some friend started lending me some tapes from them. For some reason, this same friend lent me also a tape with Wakeman's King Arthur album, and then I got to love his music too (and that later on led me to Yes, of course) There was also this song from Alan Parsons, once again the same friend showed me some music from them to get my curiosity, and an aunt in USA had som vinyls (the first two albums) which I recorded on tape (later on, I bought the albums).   Also, my grandmother had several rock vinyls which I started to borrow, and among them I got hooked with Focus's Hamburger Concerto, and Harmonium's Cinquiem Saison. I don't really remember in which order all of this things happened, but they were interwined. Then I got into Yes and found Progarchives, and from then on there was no turning back. So, in some way, Yes was the first prog band I knowingly got into.

Supertramp as well for me, & yes 21st Century Schizoid Man was life changing. My god I'd heard nothing like it.

As for legitimately getting into Prog as a genre, Rush paved the way for me about 2 and a half years ago. I'm extremely grateful and thankful for picking up albums like Permanent Waves and Hemispheres that showed me how Rock music could be so adventurous and experimental, but at the same time, did not alienate a variety of people of different tastes. That's one of the reason's why I think Rush is so special, is that they appeal to a mass body of people, without having to conforming to the requirements of the music industry for commercial benefits. I've been a Rush fan since a very young age, but I didn't start to seriously get into them until about 4 years ago when I bought the Rush gold compilation/ greatest hits, which featured many of their essential songs. I've been hooked veer since. I was big into Dream Theater and Protest The Hero at the time as well, and Floyd I had grown up with, them being on classic rock radio and what not. Rush really did it though; Genesis, Yes, Jethro Tull, Porcupine Tree followed.