Pollyanna was the “glad” girl.
She was created by Eleanor Hodgman Porter in a novel of that name published in 1913, with a sequel, Pollyanna Grows Up, in 1915.
She was an orphan, turned over, after the death of her missionary father, to live with a stern puritanical aunt.
But Pollyanna steadfastly practiced a game taught to her by her father of always finding something to be glad about, no matter how grim the immediate circumstances.
Through her continued unquenchable optimism, always seeing a bright side in every catastrophe, the entire community became infected and developed an air of friendliness.
Thus anyone who appears unduly optimistic or cheerful in the face of discouragement is now a Pollyanna.