Conversation so far:
What is Dr. Know?
Gary Miller, better known by his stage name Dr. Know, is the guitarist for Bad Brains.
What was Gary Millers role in the band Bad Brains?
Gary Miller is the guitarist for Bad Brains.
What is the significance of guitarist Dr Know?
Dr. Know is the guitarist for Bad Brains, regarded as one of punk rock's most innovative and important bands.

Question: What was his illness?
Self-contained rewrite: What was Dr. Know's illness?