When Ramses the Great died, why do you think people feared the world would end?

He ruled it ;v

Explanation:

Because he was the most "Greatest" ruler, therefor when he died; no-one knew what ( or ) who would be as "great" or "powerful" as him.

Explanation:

He is often regarded as the greatest, most celebrated, and most powerful pharaoh of the New Kingdom, itself the most powerful period of Ancient Egypt.

I think it was Harriet Tubman, as she was born a slave and understood what it meant to be a slave, she had to escape in 1849 and her motive to help slaves was a powerful one "Families should not be separated". 
She became the most famous conductor on the Underground Railroad. She helped many slaves individually as well as formed a network to help them through other activists.