Joe Hardy is the 17 year younger brother of Frank Hardy, together they are known as the Hardy boys.
From a very young age Joe and his older brother Frank have showed great interest in detective work, like their father Fenton, former NYPD officer and currently a private investigator. They solved their first case not long ago and have since become locally famous.
About a year ago the Hardy brothers' lives were changed forever when Joe's girlfriend Iola Morton was killed in a car bombing. Frank and Joe investigated and discovered that the people responsible for the killing were an international terrorist group known only as The Assassins. During their first encounter with the group, the Hardys traveled from Bayport to London, England and, having discovered that the murder of Iola was just part of a bigger plan, back again in time to stop the assassination of presidential candidate Philip Walker.
Iola's death greatly affected Joe; he became severely depressed for quite a while afterwards and, although he eventually got over her death, the memory of it still affects his personality and memories. He later starts dating Vanessa Bender upon her moving to Bayport; in at least two books, Dead of Night and True Thriller, Vanessa appears to die in an explosion. In both cases, Joe remembers Iola's death and is heartbroken that the same thing happened again. He is also haunted by Iola's memory when a clone of her is created in The Lazarus Plot and Dead of Night.
Since then the Hardys have taken their detective skills more seriously, and have fought many terrorist organizations and solved more dangerous crimes. Many times they have worked closely with The Network, a government organization dedicated to fighting The Assassins, that the Hardys first came in contact with shortly after Iola's death, when they met Network high-up Mr. Gray at Iola's funeral.
Joe has a different fighting style than his brother; he typically uses more of a boxing style, with strong punches and kicks, although he has been known to use karate from time to time.When it comes to detective skills, Joe tends to go more by his instincts and emotions (which, as both he and Frank have observed, are usually right), while Frank tends to go by logic, providing a strong balance between the two.
Joe is also a great athlete, shown to play both football and soccer, and is also a track star/sprinter.