If you could go back in time and stop any one person or group's musical career, who or what would it be?
This isn't a "go back in time and assassinate" someone question. It's just their musical career never takes off and thus any music they ever would have made is no longer in this timeline.
I won't say his name but I stopped someone's musical career once. He was an up and coming young guitarist, getting performing gigs here and there, and teaching guitar students to help pay his bills while waiting for a break. I took some lessons from him and as part of general chatting it came out that I worked with computers. He thought that was interesting and asked good questions, so I brought him some programming books. He became a full time programmer a couple months later and a very good one too. I'm glad it worked out for him, but I always wonder what we lost.
My coach used to tell the story of a really promising track and field athlete who might have had a serious shot on the world scene, but quit to play in his band called The Barenaked Ladies. I never fact checked that, so I have no idea if it was true or not. But it stuck with me because it made me think of all the people who might have been incredible in one field or another who just never gave it a shot.
"Ike At The Mike" by Howard Waldrop. Award winning short story. An elderly Dwight Eisenhower is invited to the White House. Ike famously gave up his West Point cadetship to become a jazz musician. Among the attendees honoring him is the young Elvis A. Presley, Senator from Mississippi.
This was decades ago. I don't remember the specific books but they were about programming in C. By now that is considered a neckbeard language. The first thing the guy did, with like zero experience, was write a video compression program in C.