Dean Winchester was a hunter from an alternate timeline where John Winchester disappeared in 2003.
History
After Dean wishes on the Baozhu in the hope of ridding Michael from his mind, it instead brings John Winchester from 2003. As a result, an alternate timeline is created where Dean continues hunting, while Sam remains at Stanford and becomes a successful lawyer.
Dean's wanted poster.
In this timeline, due to hunting, Dean is considered a criminal and is wanted for assault, murder and credit card fraud. After main timeline Dean looks himself up, he learns he is known for "a lot of beheadings." The reward for help to capture him is $100,000.
When John is returned to 2003, this timeline ceases to exist, erasing this version of Dean Winchester from existence.