First Appearance: Invaders #7 (July 1976).
Appearances: Invaders v1 #7, 18, 19, Captain America #215, 253, Citizen V and the V-Battalion v2 #1.
Years Active: 1914?-present.
British nobleman Montgomery, Lord Falsworth put on a costume (no further details on his origin have ever been shown) and became the Union Jack (I), an operative for the British government during World War One. He fought a one-man commando war against the Germans and their allies during the war and became widely feard by them. At some point during the war he teamed up with various other costumed heroes to form the Freedom's Five. During the war Lord Falsworth and the other members of the Five fought against a number of German enemies, including the vampire Baron Blood. Near the end of the war Lord Falsworth was investigating the murder of a number of leading British subjects and discovered that the murderer was Baron Blood. Falsworth and Blood fought yet again, and Falsworth stabbed the vampire with a silver knife, forcing Blood to flee. A few weeks later, when the war ended, Falsworth officially retired from active government service as the Union Jack (I).
He stayed retired through the 1920s and 1930s, briefly returning to action in 1942 as a member of the Invaders. Falsworth was crippled during a battle with Baron Blood and so permanently retired as the Union Jack, although he had the consolation of knowing that his son, Brian Falsworth, carried on the family tradition as Union Jack (II), and that his daughter Jacqueline did likewise as Spitfire. After WW2 Lord Falsworth financially supported the V-Battalion, and apparently continued to do so even after the death of his son Brian in 1953.
Montgomery, Lord Falsworth survived to the modern era, when he died after helping his old friend Captain America (I) defeat Baron Blood for good.
Note: Thanks to Michael Norwitz for pointing me towards the picture on the right, which is a really neat rendition of Union Jack's pulp-style costume during World War One. Michael tells me it's from the Ben Raab/John Cassidy Union Jack miniseries.