The Amazing Spider-Man
Some many years ago, Doctor Curtis "Curt" Connors lost his right arm up to its elbow. As would be expected, this greatly affected him emotionally, and so Connors endeavored to find a "cure".
Dr. Connors soon came to be a scientist working at Oscorp Industries, and he met Richard Parker, a fellow employee, who wished to help Connors in his search for a cure. Though, the day that Richard and his wife, Mary, mysteriously went missing, Dr. Connors decided to totally shut down his work indefinitely. Years later, while working with some interns at Oscorp Tower, Curt Connors encountered Peter Parker, whom impressed him due to his knowledge beyond most teenagers. During this encounter, Connors did not find his name, but just thought him to be another intern.
A few days later, Peter came to Dr. Connors' house. Connors recognized Peter from the other day and, assuming he wanted an autograph, was quick to ask him to leave. However, Peter introduced himself as Richard Parker's son, and the scientist invited him in. They discussed the work that Peter's father and Dr. Connors were in, and why Connors had not approached the Parkers before. Peter proceeds to give the scientist his father's "decay rate algorithm", something he had been working on before his disappearance.
Later, Dr. Ratha, a colleague of Connors', approaches him, requesting him that he quickly find a cure for their dying boss, Norman Osborn. Dr. Connors agreeing to do what he can, Ratha leaves.
The following day, Peter met again with Dr. Connors in the scientist's laboratory. Peter proceeded to enter the decay rate algorithm in to a computer, with a hypothetical mouse being the target, but it fails to work at first. Peter continues to do it, finally getting a successful result that enables the mouse, named Fred, to grow an extra limb. Dr. Ratha approaches Connors, having seen the effects of Peter's decay rate algorithm, demanding that he starts human trials straight away, if they're to treat their dying employer. At first, Dr. Connors refuses to test people with the formula, causing him to be fired. Dr. Ratha decides to use the serum at a Veterans Administration hospital, under the guise of a flu shot. Connors, desperate to impress, injects the formula in to himself instead. Nothing happens immediately, and Curt falls asleep. When he awakes, his limb has fully regrown.
The scientist hears about Ratha's plan to inject the formula as a flu shot, and raced to intercept him. Along the way, Dr. Connors' arm, the one that regenerated, started to turn green and scaly. Just as he reaches the Williamsburg Bridge, he fully transforms in to a giant, mutated man-lizard hybrid. Unable to control his alter ego, Connors flips cars over the side of the bridge, the occupants only to be saved by Spider-Man.
The Lizard goes to the sewers, near to where Dr. Connors has constructed an underground lab. Spider-Man, having the suspicion that the Lizard is Dr. Connors himself, follows him. He proceeds to take a picture of the Lizard, via means of carefully-placed webs, but the camera is destroyed by the Lizard, not before he reads the camera's owner's name. Dr. Connors, as the Lizard, follows Peter Parker to his school. After ripping through the school to find him, the two finally engage in a battle. While Spider-Man's webs subdue the Lizard, they ultimately fail to do any harm.
After a quick battle, the Lizard runs through the streets of Manhattan. Aiming to reach Oscorp Tower, he finally gets there, having turned some police officers that subdued him in to lizard-men. The scientist-turned-lizard tries to get a machine that will release a toxic cloud, causing all humans to turn to a lizard-hybrid, like him. Gwen Stacy, his protégée, tries to stop him from taking it, but he wins over, not wanting to harm her.
Dr. Connors climbs to the top of Oscorp Tower, planning to release a gaseous cloud turning the human race in to lizard cross-species. Before he can do this, Spider-Man arrives. The two proceed to fight. George Stacy, captain of the police force, assists Spider-Man, knowing his true identity. Captain Stacy uses a shotgun to injure the Lizard, but this does next to nothing to the huge beast. Dr. Connors, not having control of his mind, stabs the cop with his claws.
Meanwhile, Spider-Man finally reaches the peak of the tower, and is able to replace the machine with an antidote to Connors' serum. Peter releases the cloud, causing the Lizard to turn back to an injured Dr. Connors, as well as changing the former police that became cross-species.
Following the ordeal, Dr. Connors is locked up in Beloit Psychiatric Hospital. He is visited by a mysterious man, seemingly familiar to the scientist. The man asks if Connors told Peter the truth about his father, but Curt demands Peter be left alone before the man mysteriously disappears.
The trial of Dr. Curt Connors came to an end as the former geneticist for Oscorp Industries was found guilty on all twenty counts for which he was indicted, including the murder of NYPD Captain George Stacy. Connors and his attorney, Anne Weying, were unable to convince the jury that he was not responsible for his deadly actions while transformed. His defense that he only injected himself with the serum that changed him into the Lizard to prevent Oscorp Industries from experimenting on innocent civilians did not sway the jury.
Next stop: Rikers. But even that is controversial. Ravencroft Institute for the Criminally Insane has said their facility is better served for housing and studying a prisoner such as Connors, but the judge has yet to rule on where Curt Connors will spend what is likely to be the rest of his life.
Spider-Man: No Way Home
At some point from before he was cured, the Lizard was transported to another universe after a spell casted by Doctor Strange goes haywire. Connors hid in the sewers until he was confronted by Strange and transported to the Sanctum Sanctorum and locked inside a dungeon. Later on he would reunite with Max Dillon as they were both workers in the Oscorp Industries. Eventually he, Dillon and three other villains from a third separate universe would be released from imprisonment by the Peter Parker from the current universe in order to help cure the villains from their destructive powers and to spare them from dying by Spider-Man in their universes before "going home". All the villains except Connors would group in Happy Hogan's apartment while he remained in a F.E.A.S.T truck.
Shortly after Green Goblin battles Peter, Connors finds an opportunity to escape the truck and join the fight before escaping along with the other villains. He would later join Dillon (as a reformed Electro), and Sandman in a final battle with three Spider-Men, one that was originally from the same universe. The Peter Parker from his universe developed the cure he made before to cure Connors and with the help of the other Spider-Men was able to cure him once again. When the Green Goblin collapsed the scaffolding that they were fighting on, Connors nearly fell to his death before he was caught by the Spider-Man from the Goblin's universe. Later, Doctor Strange casted a new spell that made everyone forget his universe's Peter Parker and sent everyone from another universe back home, including Connors.