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.
Timberlake, Bieber, or the Canadian PM who kept the country from bankruptcy despite the blinkered conservatives and their expendable constituents trying to kill the country and all its inhabitants on the daily?