Often conveys sadness or sympathy for someone's decline in ability or health. Since her illness, she's been a shadow of her former self, struggling to engage in the sports she loves.
Pro Tip 2/3
Not Literal
Used figuratively to express a significant change, not to suggest someone is an actual shadow. Jim used to be the life of the party, but now he's a shadow of his former self.
Pro Tip 3/3
Change Over Time
Implies a decline from a previous state, often gradually or due to specific events. The athlete was a shadow of his former self after his long break from training.