He is my friend who specializes in the study of Teichmüller theory, particularly focusing on surfaces of infinite type. His approach lies in the field of quasiconformal mapping theory, and he often imparts me a complex analytic perspective on Teichmüller theory.
He is my colleague sharing a research room, majoring in a surface-knot theory. I often talk with him about not only mathematics but also other topics (food, hobby, etc).