Krautrock (probably Neu) was definitely what first made me understand the power of repetition.
Velvet Underground is the first, but it's true the Moe Tucker was more of a metronome than repetition as such
Dinger + Jaki Liebezeit (and maybe Werner Diermaier) are really the ones
Dinger was as noted a monomanical weirdo, just totally sui generis
but Liebezeit deliberately came to minimalism and repetition by stripping everything away from free jazz except the freedom
I'm sure I've posted this on Dissensus before, Jaki telling the amusing and extremely 60s anecdote of how he arrived at monotony