Hulk read picture book about Hydra when he joined group.
Hulk shown that Hydra has been smashing since 2686 to 2613 BC
Hulk given link for people who can read to know about Hydra and all the wonderful work they have done :~)
https://en.wikipedia.org/wiki/Hydra_(comics)#Fictional_organization_history
Hulk Hail Hydra