Answer:
He was known for making mockery of people from other races.
Step-by-step explanation:
Dr. Seuss gained his popularity as the author of bet-sellers children's books (such as the cat in the hat and How the Grinch Stole Christmas!).
He gained his popularity in 1950s, and many of his views were considered to be very questionable if we look at it from the modern's perspective.
For example, he made a lot of mockery for the people who live in Africa and East Asia, promoting the idea that white civilizations generally better compared to the other.