Molly Mayne was born to a large Irish family in the late 1920's, the only girl of six children. An athletic girl, Molly easily outpaced her brothers and in school, routinely outshone her male peers. As a result, she was labeled a tomboy and men found her intensity too much to take. Molly was left alone as other girls fulfilled the normal roles of growing women in the 1940's. After high school, Molly tried to tone down her un-feminine image by taking a secretarial position at Gotham radio station WXYZ. There she became infatuated with the heroic image of Green Lantern and fantasized that she would appreciate a woman of strength and character. She broached the subject to her supervisor, broadcaster Alan Scott, when the radio station hit on the idea of a radio show with a Green Lantern serial. Scott dismissed the idea and suggested that Green Lantern only had attention to devote to criminals.

    As part of the radio serial, the station came up with a recurring villain known as The Harlequin who would taunt Green Lantern each week. Seeing the need to attract Green Lantern's attention and gifted with a natural athletic prowess, Mayne developed a costume and took to the Gotham rooftops as the Harlequin. Obtaining a pair of special glasses and a flying car from a secret source, she approached the Gotham criminal establishment and attempted to form her own gang. After the recent arrest of Kid Killem, his gang was known to be leaderless and the Harlequin seized the opportunity to make her grand entrance. After an initial melee with the gang, she convinced them of her ability to lead. Her takeover was interrupted by the sudden arrival of Green Lantern. As the gang watched, the Harlequin bested the astonished hero, pushing him out an open window where his descent was stopped only by a flagpole. While the gang recovered, she quickly lowered the hero to the ground and made her getaway.

The next day, while Green Lantern made his radio debut, the Harlequin and her gang made a daring bank robbery. Breaking away from the station, Green Lantern intercepted the gang and in a battle broadcast to thousands, was captured and taken to the Harlequin's hideaway. After making the hero comfortable (though bound), the Harlequin thought of her next crime. She was horrified when one of her gang informed her he had already arranged a distraction: a bomb in Lentil's Department store. Rather than allow hundreds to perish, the Harlequin assaulted her own gang only to be captured herself. As the villains made off with their captive former leader, Green Lantern surreptitiously used his power ring to switch places with her and attacked the crooks as the sped along a New York highway. The Harlequin meanwhile made her way to Lentil's to defuse the bomb. Arriving too late to help, Green Lantern hurriedly evacuated the building just before the store exploded, leaving the Harlequin supposedly dead among the rubble. Though a search turned up nothing, the world assumed it had seen the last of the Green Lantern's first female adversary (All-American Comics #89).