Legionnaire was a founding member of the Knights.
Legionnaire is Colette Marceau, a French woman who was an actual member of the Légion étrangère (French Foreign Legion) and a spy during World War I, who then adopted the title Legionnaire for her superhero work prior to and during World War II.
Following the tragic end of World War II and the loss of several teammates, Legionnaire quit the Knights and took several years off. Always known for her exceptional beauty, Marceau even worked for several years in Paris as a model for the elite fashion houses. Growing bored and restless, she then returned to work as Legionnaire in the 1950s, this time as a solo adventurer as she had been prior to World War II.
Though largely retired in the past decade, Legionnaire is still alive (her longevity due to a spell by Dr. Darke) and active. She recently refused to return to the Knights following the events of the Darke Day.