The Lizard Gas was developed by Dr. Curt Connors and was planned to be used on all the citizens of Manhattan.
The lizard serum was developed originally as a liquid and was later converted into a gas, and was planned to be used as a cure for Connors' missing arm and Norman Osborn's retroviral hypoplasia when successfully developed. It was also going to be distributed worldwide as a cure for any disease by granting humans the regenerating ability of a lizard.
When Connors had started developing this miracle serum (using the facilities and resources of Oscorp) he was told by Rajit Ratha that he had to have human trials, (testing the chemical on humans) as soon as possible so that they could save Norman Osborn from his illness. Connors reply was "People die, even Norman Osborn... and where on earth are you going to find the people to volunteer!?" in response to this Ratha threatened to fire him, Connors had no choice but to test it on himself. This had at what first appeared as a positive outcome as Connors grew a new arm but after in a matter of seconds, as the seconds turned into minutes the lizard DNA began to take control (whilst in the back of a taxi) transforming him into the reptilian-humanoid creature known as the "Lizard". He rampaged the city in anger of this, and eventually set up an underground makeshift lab in the sewers where he could work in peace from civilization and learn more about the newfound abilities that this Lizard serum had granted him. He made a video diary saying that it had sharpened his senses, quotes: "Subject no longer requires glasses" and a great increase in strength and speed.
The thought then came into Connors' mind that this could be the next stage in human evolution, that this accidentally created Lizard creature is a superior species to our own. And so he worked on, developing it into a gas so that it could distribute citywide with the use of the "Ganali Device" atop of the tallest building in Manhattan (Oscorp) and so he made his way there (in the form of the Lizard). On his first arrival to the surface of the city, he was met by a S.W.A.T team who fired rounds of gunfire at him having no effect thanks to his tough reptilian skin and rapid healing/regenerating ability. In response to this, he killed and injured a few of them and released the Lizard serum in its new gas form from canisters he had in a sachet bag he was carrying.
He then started his climb of Oscorp and halfway up tore his way into the floor of his office (to retrieve the ganali device) only to discover it was gone. However, sensing the presence of someone else he soon found it hidden in a vent along with Gwen Stacy holding it who he took from with ease. When reaching the top he placed the test tube containing the lizard serum which automatically went onto a two-minute timer. He was then faced with the defeat of a battle against both Spider-Man and George Stacy who sacrificed himself in-order for Spider-Man to place the reptilian antidote in the ganali device which Spider-Man did 1 second before the Lizard gas was to be released; Lizard unaware of this figured it out when the cloud dispersed from the device was blue instead of green the color it should have been, after this the raining antidote turned Lizard back into human form.
Video game Epilogue
In the game Curt Connors recreates the lizard serum within his makeshift lab (much to the dismay of Gwen) so that he can turn into Lizard in order to help Spider-Man bring down the S-Bots terrorizing the streets of Manhattan. The Lizard serum has not been used since.