Dr Thaddeus Sivana is the main antagonist of the film Shazam!. He is a vengeful scientist who was rejected by the Wizard Shazam and is bent on stealing Billy Batson's powers for himself to unleash chaos on the world.
In 1974, a young Thaddeus Sivana was in a car with his father and brother Sid while on a trip to his grandfather's, where he was being mocked by the both of them for playing with an 8-Ball. Suddenly, the ball begins to show Sivana a series of symbols, resulting in him being transported to the Rock of Eternity, where he meets the Wizard Shazam. The Wizard explains to the young Sivana that he had spent centuries searching for a new champion to inherit his powers (after his first turned evil and unleashed the Seven Deadly Sins upon the ancient world), and that to do so he must be "pure of heart" and thus immune to the Sin's temptations.
However, the Sins, now trapped in statues within the Rock, manage to persuade Sivana to think that the Wizard is lying to him and that they can give him power if he frees the Eye of Sins. As Sivana attempts to do so, the Wizard stops him and angrily states that he will never be worthy enough to be champion, sending him back to his father's car. Sivana, confused at being sent back and frustrated with not being chosen as champion, causes a scene in the car that ends in an accident, leaving his father crippled and even more resentful towards him. At the same time, Sivana spots a message in his 8-Ball stating "find us" (presumably sent by the Sins), resulting in him dedicating his life to trying to unlock the secrets of magic and return to the Rock.
Years later, Sivana becomes a physician at his father's company, Sivana Industries (though he is still dismissed and undermined by his family), where he funds Dr. Lynn Crosby's research on those who were approached by the Wizard to become champion under the pretenses of a study on "mass hysteria". During one interview with a woman who was summoned by the Wizard, Sivana watches a recording of the moment she was taken to the Rock and ends the interview afterward. Sivana heads back to his office with Dr. Crosby demanding an explanation from him, causing him to reveal the truth behind her research and that he has realized from the woman's footage that the symbols needed to open the door to the Rock repeat themselves seven times.
After writing the symbols out on the door to his childhood room, Sivana believes that he has finally created a gateway back to the Rock, though Dr. Crosby doubts him; however, in doing so, she puts her hand on the door frame and ends up disintegrating, thus confirming Sivana's belief. He proceeds to return to the Rock, where he meets the Wizard again, asking him if he remembers who he is. The Wizard does so and demands that Sivana leave as he is not worthy to wield his power, though Sivana rebuffs him, asking if he knows what telling a child that they are not good enough does to them. Deeming himself not pure of heart like the Wizard said, Sivana takes the Eye of Sin, resulting in it fusing to him and replacing his left eye, much to the former's horror.
As a result, the Sins are freed from their imprisonment and enter the Eye of Sins as the Wizard attempts to stop Sivana, only to be blasted and defeated by the latter's lightning instead. Sivana then leaves the Rock with the Sins in tow, while also leaving the Wizard behind. Realizing the threat at hand, the Wizard quickly finds a new champion in the form of Billy Batson, whom he bestows with his abilities, transforming the boy into an adult superhero, before seemingly dying and fading away.
The next day, Sivana returns to Sivana Industries and interrupts a board meeting held by his father and brother. Locking the door and ignoring his father's order for him to leave, Sivana goes on to state that he has always looked down on him even before the accident that cost him his legs and that he now has proof of everything he had claimed during the said accident as well. Sid confronts Sivana and threatens to throw him out of the room, and in response, Sivana hands him the 8-Ball and tells him to ask it what his chances are of doing so. As Sid and the other board members laugh him off, Sivana suddenly grabs his brother and throws him out the window to his death, remarking that his chances were "not good".
Following this, Sivana unleashes the Sins from his eye and uses them to slaughter the remaining board members, leaving only his father alive. As his father cowardly begs for Sivana to spare him, offering to give him everything from wealth to the entire company, Sivana points out his greed and sarcastically remarks if he thinks any of the materials he has accumulated give him "real power", stating that the power given to him by the Sins is real power and that only he has it. Right after this, the Sins alert Sivana to the fact that the Wizard has chosen a new champion and that he must kill him before he realizes how to harness his abilities, which Sivana agrees to do. He then recalls the other Sins and leaves the room, leaving Greed behind to kill his father. Inside the elevator leading to the bottom floor of the building, Sivana sees an ad for Sivana Industries ironically claiming that the company values family over all else, and smashes the screen showing the ad in rage.
Later, Sivana is drawn to Shazam after he accidentally causes a bus to crash and subsequently saves it, enraging his foster brother Freddy and getting him to call him out for misusing his powers in the process. Approaching Shazam, Sivana demands that he give him his powers, though Shazam brushes him off until he is punched and knocked into a car. Sivana goes on to state that the only thing that can hurt a magical being is magic while electrocuting two police officers and again demands that Shazam hand over his power. However, Shazam punches him in the groin instead and arrogantly begins taunting him, driving an enraged Sivana to drag him into the atmosphere. As a frightened Shazam tries to apologize, Sivana remarks that he is groveling like a child, with Shazam remarking that he actually is one before being thrown to the ground. Shazam saves himself by realizing how to fly at the last minute, although Sivana continues to attack him.
Sivana and Shazam's battle takes them to a mall, where Shazam ultimately retreats to running away upon realizing that he can't beat Sivana, transforming back into Billy Batson and escaping into the panicked crowd in the mall before he can be caught. However, Freddy appears and begins yelling out to Billy, and Sivana, while watching news coverage of Freddy and Shazam's earlier falling out, deduces that Freddy knows who he really is. Sivana captures Freddy (who immediately recognizes him as a "supervillain") and uses the boy to lead him back to the Vasquez household, where he meets Billy's other foster siblings and captures them. After finding out the truth from his biological mother about why she abandoned him, Billy receives a call from Freddy and apologizes for his behavior, only to find Sivana on the other end, asking him to come home. Billy quickly transforms back into Shazam and rushes off to the Vasquez house, where he finds Sivana holding his foster siblings captive.
Sivana unleashes the Sins from his eye and forces Billy to comply with his demands by threatening to kill his family, making him reluctantly agree to give up his powers. Once Sivana takes Shazam to the Rock of Eternity, Sivana punches him over to the Wizard's former throne and forces him to hand over the latter's staff so he can use it to transfer his powers. Shazam attempts to reason with Sivana by stating that he knows how he feels about chasing something that he thinks will make him finally good enough (relating his quest for power to his own search for his mother) while also pointing out that the Sins are merely using him for their own ends, though Sivana ignores him. Before Shazam can transfer his power, his foster siblings arrive to stop Sivana with makeshift weapons, Freddy hitting him with his replica Batarang, which, to Shazam's surprise, leaves a gash on his head that heals as soon as the demons return into his body. Before Sivana can attack his family, Shazam stabs him with the Batarang and throws him into a wall, knocking him out.
Shazam and his siblings rush to escape from the Rock with Sivana in pursuit, eventually fleeing when the former remembers how he left the Rock last time, quickly imagining himself and his siblings inside the "Gentleman's Club" he visited earlier. Shazam and the others run off to the Winter Carnival, where the former accidentally draws Sivana by transforming back to Billy Batson. Sivana hovers over the crowd and calls Billy out for hiding behind innocents like a coward, and tries to bait his enemy out by causing the Ferris Wheel to tip after the crowd starts to disperse (due to the mall Santa that he and Shazam had frightened earlier starting a panic). Deeming that he has to save his family, Billy transforms back into Shazam and confronts Sivana, while Mary and the others deduce that Sivana gets his power from the Sins and that he is weakened when they leave his body.
In order to help Shazam, Mary and the others goad Sivana into setting the Sins free to chase them while he and Shazam fight, resulting in the latter turning back into Billy to escape him, only to end up being drowned in a pool of water by him instead. Mary attempts to shoot Sivana with a BB gun, which distracts him long enough for Billy to get out of the water and transform, though she ends up being captured by Gluttony in doing so. With all the children captured by the Sins, Sivana again tries to force Shazam to surrender his power; however, before he does so, Shazam recalls what the Wizard had said about sharing his power and that his champion was to help rebuild his council, and thus knocks Sivana away and uses the staff to turn his family into heroes like himself before breaking it. Enraged, Sivana unleashes the Sins to fight Shazam's family while he takes him on by himself with their battle leading them into the city.
While on a roof with Sivana, Shazam notes that only six of the seven Sins have been released, and cleverly goads the final Sin, Envy, into leaving Sivana's body, stripping the latter of all his remaining power. Sivana begins to plummet, though Shazam saves him after using his lightning to deal with Envy. Shazam flies back to the carnival with Sivana and takes him to the downed Ferris Wheel, where he forcibly removes the Eye of Sins from him, both returning him to normal and entrapping the Sins once again. Shazam and his family then return the Eye to the Rock, keeping it from Sivana for good.
Sometime after being convicted for his crimes, Sivana is seen inside his prison cell, drawing out the symbols meant to open a door to the Rock over and over in an effort to free himself. However, the chalk he is writing with breaks, causing him to have a meltdown. To his confusion, Sivana then begins to hear a voice mocking him and turns around to see Mister Mind; an evil alien worm that had escaped from the Wizard's captivity when he had freed the Sins. Mind informs him that there are more ways to acquire magic "than the mind can imagine", and that, together, they will soon take over the Seven Realms.