David Hatter had spent his whole adult life with a foot in each world. The Queen's world of Instant Gratification, and the harsher world of those that opposed her.
Running a tea shop came naturally to Hatter; after his mother ran off, his father spent all they had at them. He grew to manhood watching people drown themselves in synthetic emotion... and he had joined them.
He'd always had a sixth sense for what his customers needed. He knew their pains, for they filled his heart as well. He despised himself for indulging, never really alive. His father had gone mad from consuming Happiness daily, and had spent his last years in the Hospital of Dreams.
Since his father's death, Hatter used every ounce of willpower to control his addiction. A few drops here and there to get through the day.
It had been a long day... Cold and dreary, few customers, and fewer that could pay. When Ratty slunk towards the shop claiming he had a trade, Hatter had just sighed. When the foul smelling cretin shuffled away to collect his trade (some ridiculous Alice story), Hatter added a few drops of Generosity to his tea. Ratty was getting old and had nothing of value, but Hatter had an image to maintain. A few words in the wrong ears from Ratty, and he could lose business. He felt better after sipping his tea; his headphones sending a gentle melody towards him from their place on his chair.
The girl was an Oyster, he'd have helped her regardless of her name. But when he'd turned around and looked into her eyes, he knew she was special; Alice or not. The Generosity was flowing through him now, filling him with good intentions and the desire to do anything for this girl. His payment from Dodo also gave him plenty of incentive, if that ring on her finger wound up being valuable.
But when the time came, and the gun was aimed at him and his Tea had worn off, Hatter regretted nothing. He looked at the girl, Alice, and knew he'd do anything to protect her. A raw surge of real emotion shot through him. Later, when he was staring down the comically hideous ceramic rabbit-head that Mad March the assassin currently wore as a face, the only thought in his head had been that he needed to get to Alice. She was all that mattered.
After the battle was finished, and Alice had gone back to her own world, Hatter sat down in his wreckage of a home, and saw a broken bottle laying beneath a chair. It still had an emotion in it. When he flipped it over and read the word "Happiness", he poured the contents onto the grass. He knew it would never measure up to the feeling of holding Alice close to his heart.
David Hatter ran through the Mirror, and never looked back.