King Crimson’s thesis—that rock music could be tirelessly complex and still punch you in the gut—constituted a new branch on rock’s evolutionary tree, setting the course for a certain strain of prog and metal that continues to unfold. From Meshuggah’s whiplash time changes to the suite-like compositions of Dream Theater, from the ornery funk of Primus to the sheer grandeur of Mastodon: If it stretches the limits of what guitar-based music can do without so much as cracking a smile, you can probably trace it back to King Crimson.