Benefactor is someone who gives people gifts usually in form of money or charity or via an organization.
"That man is so many people's benefactor, he has helped a lot."
Beneficiary is someone who benefits or receives an advantage.
A benefactor is a person who selflessly provides financial support to someone in need.
“I couldn’t have made it through medical school without the help from my benefactor.”
A beneficiary is the person who receives money after someone dies.
“Because Carlos doesn’t have any children, he will name his nephew as beneficiary in his will.”