I learn a lot of Maths and other things from Christopher Douglas who also supervised my PhD.
I learned a lot of Computer Science from Samson Abramsky who supervised the first part of my PhD.
From undergrad to post-grad to post-doc, I've talked a lot of Maths with David Reutter.
More awesome people:
Christoph Weis whose coffee making skills and spectral sequence computations are unrivalled,
Jan Steinebrunner who asks all the questions and then tells you the answer,
My partner Chloé Colson does Maths too!