Belle St. Claire, then called Belle Colbert, was once a country singer just starting her career when she met Ven St. Claire. While both were young and shy, they fell in love and eventually married. Belle even had Ven's child, Ben. Sadly, an amusement ride in Ven's latest theme park malfunctioned, killing Belle and leading to the eventual collapse of Ven's sanity. Ever since then, Ven had vowed to revive his wife in any way he could, even if it is through amoral or immoral means.
When Penelope was used as a vessel for Belle, it was only a matter of time until Belle realized what was going on. By the time she saw how crazy her husband had become and the terrible things he had to do to see her again, she became terrified and broke down in tears. Penelope, having enough inner-strength to break free from Belle's control over her body, forced Belle to make one final plea to the Cooper Gang. She wanted the gang to defeat her husband and stop his madness once and for all. During the boss battle with Ven, her ghost assists Bentley by pointing out flaws in Ven's voodoo-powered shield so that Bentley can shoot Explosive Darts at Ven's cybernetic stinger. After the battle, she points out the pilot goggles that Chronos left behind. These goggles would help the gang reach WW1 Netherlands. Ven St. Claire's ghost eventually came to her, his sanity having been restored upon his death.
At the end of the game, her son Ben and his aunt Gwen found the St. Claire Memorial Hospital. The press is only told that it was in honor of Belle, mainly due to Ven's impressive criminal record.
Her appearance is known to be eerily similar to Penelope's, from her tail to her face, with the only difference being that Belle is a redhead and Penelope is blonde. Upon seeing a picture of her, Sly even asked himself if this was actually Penelope. Due to her status as a ghost, most of her body has become ghost-like, including her upper body, with only her head and arms retaining their original look.
Known for her strong will, she was able to persevere despite having a terrible sickness at the time of her death. She is also quite forgiving, as she was able to forgive her husband Ven despite his terrible decisions, though even she admits it wouldn't be possible to view him the same way again. She always thinks about the family first, not once expressing any selfishness, especially when she involves Ben in discussions and arguments. Belle is extremely brave as well, confronting her husband about what he has done, despite becoming very emotional during the ordeal.
Belle, being a country singer, has the power to sing incredibly well. In fact, Belle was Sly's favorite country singer. As a ghost, she is able to float around and is completely invulnerable to attacks, as everything goes right through her. The only thing she can't go through are other ghosts.