Sondra Fuller was an agent of Kobra. She agreed to undergo an experiment involving shapeshifting because she hated her own face. She gained the shapechanging abilities of Matt Hagen, but at a much higher level. She can mimic the powers of anything she transforms into. However, unlike Hagen who returns to normal after some time and requires a particular protoplasm before he can become Clayface again, Sondra cannot return to normal, which she finds both a curse and a blessing.
As Lady Clay, she has battled the Outsiders and even formed a team with the other Clayfaces called the Mud Pack. During the events of the Mud Pack, Sondra Fuller began masquerading as the hero Looker and visited Preston at Arkham. That same night, he got into an argument with Helena and unintentionally knocked her head off. Believing he killed her, Preston went on a rampage until subdued in a nearby swamp by the Asylum guards. He was rescued by Fuller, who was still using Looker's appearance and powers, and used them to make Preston obey the commands of Basil Karlo, the first Clayface. Karlo ultimately betrayed Fuller and injected himself with Fuller's and Preston's blood. After Preston finally broke free of Fuller's control, he was about to kill her when she admitted how sorry she was for using him. The two fell in love and went on to live together in the hills outside Gotham, and Fuller became pregnant with their child, Cassius.
During Knightfall, Sondra attacked Azrael who was wearing the Bat-costume and was filling in for Batman.
Her motivation for the attack turned out to be that the villain Abattoir had kidnapped her son, Cassius Clay, and blackmailed them into returning to Gotham, where Preston should kidnap Graham while Sondra distracted Batman. The plan almost worked, but Azrael pressed the panic button on his modified costume releasing a sudden burst of energy that knocked out Sondra. He injected her with an anesthetic and left her for the police.
Meanwhile, after delivering Graham to Abbatoir, Preston double-crossed him and went after Abbatoir with the intention of killing him. His son (Cassius) meanwhile made his way to the fire escape. Batman arrived and during the fight, Abbatoir escapes and Preston breaks his legs. Meanwhile, Cassius tries to fly by morphing wings formed like his mothers. Preston tries to save him but he already jumped. Cassius almost hits some power lines, but Batman arrives and saves him. As unrelenting as he is, Az/Bat does not allow Preston to escape and the two fight and Az/Bat shoots sleep gas at him, knocking him out. It is assumed he was taken to prison.