For me, it was mainly the philosophy and politics teachers. Boy oh fucking boy, for some reason, every single one of my philosopy and PolSci teachers were... interesting personalities to say the least. It was our philosophy teacher who introduced us to the Labor Theory of Value, oddly enough, and the issue of economic inequality. And as for the PolSci-Side, two teachers stand out: One grew up in the GDR and was very, very nostalgic about it (with some fair criticisms, especially concerning the Stasi), and the second, and final one in my case, was an irony-poisoned super-leftist with a gigantic disdain for the rich, the state and capitalism.
I had a Biopsych professor like that. Cool ass dude RIP Terry.
Edit: as far as teachers that radicalized me it was my biology professor. He was like a radical guerrilla environmentalist who would take us off trail on field studies to go rip up invasive species. Every cool STEM guy is an anarchist I swear. He was also way ahead of the curve and was one of the early voices warning of insect populations declining. That shit still haunts me.