Chimpanzees! I went to Kibale National Park back in 1999. At that time, they were just habituating a group of Chimpanzees to be used to tourists.
The activity at that time was essentially to chase chimpanzees through the jungle as they ran away. Eventually they would climb trees and watch us from above.
Tourists did that for years until the chimpanzees got used to people running after them. Then they would just stop running and watch you closer.
Anyway, 22 years later, I returned. Wow they are way more calm around people now. They walk right next to you and go about their lives with no fear of tourists.
Kibale National Park - Uganda