Pangloss is a noun that refers to a person who is optimistic regardless of the circumstances.
Panglass was a character in an 18th century novel by Voltaire called Candide. The character was known for remaining upbeat and optimistic even when things were going catastrophically wrong. It’s important not to use the word to describe an ordinary optimist, but someone whose optimism has reached foolish levels.
I like Janet, but she can be something of a pangloss. No matter how badly things are going, she always thinks they’ll work out for the best.