Gregor Samsa is the protagonist of The Metamorphosis by Franz Kafka, and when we first meet him he has been transformed overnight into a giant (and rather hideous) bug, something like a cockroach. While his body is that of a bug, his mind is still quite human and we are privy to all of his thoughts. Even worse, Gregor still feels and has emotions, so when his family and others begin to recoil from him in horror and even cruelly torment and abuse him, we feel his pain.
Gregor has two things which seem to be the primary building blocks of his identity, and they are ultimately connected. The first essential aspect of Gregor's character is his job; the second is his consuming need to provide for his family.
Gregor is a traveling salesman who has been a faithful and productive worker. Though he hates his job, it is the means to supporting his family. His job is horrible and unsatisfying in nearly every way, and in fact Gregor considers committing suicide because he is so discouraged and unfulfilled.
Perhaps it would have been bearable for him if his family had appreciated his efforts, but the truth is that they consistently took advantage of him. The Samsas (except for Gregor) lived quite well. They had servants to help cook and clean, and none of them had to work. They all ate fine food and blithely enjoyed a life of leisure at Gregor's expense.
At first we wonder whether the family is incapable of working on their own behalf, but it does not take long to learn that they are all perfectly capable of fending for themselves if they have to. Even worse, Gregor is not just working to meet his family's needs now, but he is paying off his father's debts from a failed business deal--and his father is living a leisurely life as he lets Gregor work himself to death on his father's behalf.
Gregor obviously cannot work now that he is a bug; in fact, he can barely get himself out of his bed. Though he has been a faithful, reliable, and productive worker for five years, the one day Gregor does not show up for work someone from the company arrives at his house, demanding a satisfactory explanation for Gregor's absence.
This kind of work and treatment is so far from what Gregor wanted for himself, and we have clear evidence that at one time things were different for poor Gregor.
On the wall directly opposite hung a photograph of Gregor from his army days in a lieutenant's uniform, his hand on his sword, a carefree smile on his lips, demanding respect for his bearing and rank.
Now Gregor has become a slave to a job he hates and a weighty responsibility that is not really his to bear. It is not who he was, but this is the identity which has shaped him--and which eventually kills him. He is forced to be what he does not want to be, but he conforms to the needs of his job until he can do it no longer. This job and therefore the provision for his family consume Gregor until there is nothing left of who he once was or had the potential to be.
The worst of it all, of course, is that it was all unnecessary, as his family is perfectly capable of taking care of themselves without Gregor's ultimate sacrifice. When things start to get tight, all three of Gregor's family members become productive. Gregor's father gets a job at the bank, his mother takes in boarders and does much of her own housework, and his sister also gets a job.