Rules in robots.txt target bots by this name (the User-agent: line). Some names, like Google-Extended and Applebot-Extended, aren't separate crawlers at all: they are tokens that control how content already crawled may be used.
Glossary
User agent
The name a browser or bot sends with every request, such as “OAI-SearchBot” or “Googlebot”.
Be the first name owners find.
Run the free check, then press Optimize. Then back to the dogs.