My most-recent character was an Abjurer named Belarius ("Bells," for short). Eberron campaign, Mark of Passage human.
Bells served in the Last War as high-ranking officer for House Orien. He was a 20th level wizard back in those days, but he fell on hard times after the war. He struggled with depression and PTSD, then struggled with drug addiction as he tried to cope.
His trauma and drug habit cost him everything--all his money, his belongings, his friends, his spellbook, and even his freedom when he turned to petty theft to feed his habit. While he was incarcerated, drug withdrawal and a mental breakdown took a heavy toll on him, and he forgot himself and almost all of his training. When he was finally released, he returned to his house only to find his wife had moved out. She had left a note, explaining that she had to sell the house in order to pay his legal fees, but she left him a gift in the closet. It was a blank spellbook. "For your fresh start," she had written in the inside cover. "Find me in Sharn when you're ready."
So he was a 1st level wizard again...he only remembered a couple of cantrips and some first-level spells. But he was clean again, and he was keen to become a better man--the kind of man his wife deserved. He joined an adventuring party, and began looking for opportunities to better himself and make the world a brighter place.
It was an interesting twist on "learning" magic--rather than learning new stuff every time he gained a level, he was remembering stuff that he had forgotten or blocked out of memory.
He eventually got all of his memories back, faced the demons in his past that had driven him to the brink of madness, and found his confidence again. He became a hero of some renown, as well, when his team of adventurers defeated the Lords of Dust just a few months after his release from prison. When the campaign ended, in the final scene, the party saw him walking through the gates of Sharn with a dozen roses.