-Victor Fries is born in Gotham City, son of Charles and Lorraine Fries.
-Victor develops a hobby of freezing animals. His father, a control-freak not understanding how to help his son, sends him to a boarding school. He feels detached from the rest of the world here, developing an apathy for others.
-Fries discovers the love of his life, Nora. Though she's an athelete, and him an egghead hoping to become a scientist in the field of cryonics, the two fall deeply and happily in love. They marry.
-Fries discovers Nora has been diagnosed with a rare and deadly disesase several years out of college. He takes on a job working for a drug company called GothCorp, and uses their funding to develop a method of cryogenically freezing someone perfectly.
-Victor is discovered by the CEO, Ferris Boyle, and he angrily storms into his lab, demanding that the illegal procedure be stopped. Desperate to save his wife, the two enter a fistfight, during which Fries is pushed into a series of cryogenic chemicals.
-Victor's body structure is painfully changed, terrifying Boyle enough that he flees the lab and calls the police. In the ensuing chaos, Fries manages to steal his wife's cryogenic chamber, and flees.
-Fries, feeling his body steadily become more and more susceptible to heat, develops a suit which keeps him at sub-zero temperatures at all times. Infuriated by this injustice, and terrified his wife may die, he weaponizes his cryonics systems, creating a suit with super-strength and durability, as well as a gun capable of freezing objects or firing ice with deadly force.
-Dubbing himself Mr. Freeze, Fries goes on a rampage through Gotham, looking to steal the funds of Gothcorp to fund his research again, killing anyone who stands in his way. He nearly kills Boyle, when Batman stops him, discovering the truth of the situation, and sending Boyle to jail with evidence he'd managed to scrounge from GothCorp's libraries.
-Fries is interred in Arkham Asylum, Nora's whereabouts undiscovered by others. Eventually he escapes, and finds that now that Boyle is rotting in prison, his desire for revenge is unquenched. He now seeks to spread misery wherever he can, as long as it furthers him towards his goal of saving his wife. He is a man obsessed.
Mr. Freeze, fittingly, has a personality best described as "cold". He views the world with detatchment from his fellow humans, not viewing himself as the same as them. He does not see himself as above or below them, instead finding himself somewhere separate, yet equal. He is alien to most people, and subsequently they are alien to him. He feels no kindness or sympathy, gives no charity, and feels no sense of honor. All he wants is vengeance; and since his vengeance against the man who made him like this was taken by the Batman, he seeks to make all others who stand in his way, or who may even be bystanders in his crimes, as miserable as he is. He does not care if he takes someone's limbs through frostbite simply because they were nearby when he robbed a jewelery store; they are not important.
Mr. Freeze obsesses over Nora. He wants to find a way to rejuvenate her, to bring her back to life and hopefully one day live a happy life with her again. He is filled with that single, desperate hope, clinging to it like a castaway to driftwood. And yet, it is impossible, and somewhere, in a part of his mind he seeks to drown out, he knows it. He hates the thought because, of course, it means the love of his life is taken, but he also hates it because he has already committed such terrible acts in the search for a cure. He suffers from the sunk cost fallacy very deeply, not realizing what is wrong in the least. And worst of all, he banishes the possibility that Nora would awaken horrified at what he's done from his mind. That is a fate he simply cannot stand.
Make no mistake, Mr. Freeze is bitter. He is bitterly frustrated at the fact that all his life he has felt imprisoned. As a child, he was stuck in a boarding school; working for GothCorp, he was trapped under Boyle's thumb, especially before his secret got out. And now, he is locked inside his suit or a specially-made cell for the rest of his life, unable to ever feel truly free. His only out, that being Nora's companionship, has been taken away from him, and his frustration has been frozen into cruel fury. He hates his life, he hates existence, and cannot fathom ever being truly happy again. Smiles on his face are mockeries of happiness, usually only worn when he gains the upper hand or quips at someone before killing them--and yes, he has /no/ qualms about killing someone, if anything viewing it as cruel mercy, removing them from this terrible world. He is not convinced that there is happiness to be found for him, or anyone else, no matter where he goes, and the sight of laughter only serves to anger him.
Mr. Freeze seeks no friendship, and can offer none in return. If he allies with another person, it is exclusively so that he can gain from it, and if they have nothing to offer, neither does he. As a result, most of the people he works with are either thugs or villains; thugs because they want a cut of the profits, villains because they seek to use him, and offer him money or power in return. It's getting harder to find people willing to work with him nowadays; many thugs have seen that, when injured or suffering from the cold, he's willing to leave them behind and forget them, knowing it's very close to a death sentence to hang around him too long. The fact that he has a propensity for diamonds and cash, however, as opposed to simply killing people randomly or stealing odd items, means that the desperate and destitute will seek him out. It doesn't matter what reasons people have for working with him. All he wants is enough money to continue his research. People don't factor into that cost. At the very least, he gives what he owes; while he's left people to die, he's never killed men to take their cuts from them. Bad for business.