When I think influential, I think musicians who helped to create a new sound that then affected a whole wave of popular music that came after it / because of it.
So with that in mind, I'd have to start with
Elvis / Chuck Berry / Jerry Lee Lewis
then go to
The Beatles
and then
Sex Pistols
and I only say them because I don't know all that much about the history of punk. I'm betting there are others who did it earlier and louder and punk-y-er but say, when a kid these days starts listening to old school punk, they start with The Sex Pistols (IMHO)
Feel free to shoot me down but I feel like all the rock music that's ever been created has been an offshoot of these guys.
I wouldn't put U2 in here anywhere simpy because I don't think they really did anything all that revolutionary. I mean they did Achtung Baby when the world was listening to Vanilla Ice but there were others out there doing rock music still. And they did ATYCLB when everyone else was listening to Gwen Stefani, but they weren't the first ones to do 'sincere'. Yes, I know I'm simplifying but just thought I'd throw my 2 cents out there.
So have you decided to look into their other stuff, besides Who's Next? If you like the way the Who worked with synths on that, you might like Quadrophenia. Look up Bell Boy on YouTube. You may notice something about the name of the person that put it up too...
I know a bunch of there stuff. Quadrophenia is a great album btw. I still prefer Whos Next though. Love, Reign O'er Me is excellent though. Bell Boy is one of the few songs Keith sang btw.