Silver St. Cloud is a woman from Gotham City's upper class. She was involved in a romantic relationship with billionaire playboy Bruce Wayne several years ago, and at some point during their relationship she discovered that Wayne is secretly the costumed crime fighter known as the Batman. After witnessing one of Batman's battles, she realized that she could not live with the constant fear of losing him. She ended their relationship and left Gotham.
Years later, St. Cloud returned to Gotham with her then-fiancé, U.S. Senator Evan Gregory. Gregory was on a political campaign running for Governor, but he ran into some complications when his opponent turned out to be the Joker.
After being doused with the Scarecrow's fear gas, Silver rediscovered her passion for Bruce, and decided to cut off her engagement to Gregory. Right after informing Gregory of the devastating news, Silver was abducted by the Joker, who planned to use her to pressure Gregory into dropping out. Gregory went after the Joker, but he tragically lost his right arm and leg before he and Silver were rescued by Batman. Batman asked Silver to stay with Gregory while he recovers, reasoning that Gregory needed her now and that they can wait until the current crisis has passed. Silver was furious at the notion of being "loaned out" to another man. Later, Gregory dies, and she went to meet Wayne after that.
The Widening Gyre
In Batman: Widening Gyre, Silver and Wayne rekindled their relationship after Gregory's death. Silver understood Wayne's responsibilities as Batman and was more than content to have him during daytime while Gotham had him at night. Wayne seriously considered giving up the mantle and settling with Silver for good, especially since a new mask, Baphomet, had turned up and impressed both Batman and Robin with his crime fighting abilities. Wayne finally proposed to Silver and invited Baphomet to his cave to formally introduce himself and Silver to Baphomet. Baphomet then revealed himself as the villainous Onomatopoeia and instantly slit Silver's throat.
In Other Media
Silver St. Cloud makes her live-action debut in the television series Gotham. In the second season she appears as the love interest to Bruce Wayne, but is secretly an antagonist and a member of the Dumas family, working with her uncle Theo Galavan to take down the Wayne family for outing their ancestors centuries ago. However near the end of the mid-season finale she begins to develop feelings for Bruce and regret over her actions, and ultimately stalls a ceremony held by the Order of St. Dumas to kill Bruce, giving enough time for a rescue team to save him. She later escapes with her aunt Tabitha Galavan, leaving her uncle to his fate.