Many characters have appeared in the fictional series of books about The Hardy Boys.
Character history
Original series
At the beginning of the original Hardy Boys series, Frank is only 16 years old (as opposed to 18 after the revisions between 1959 and 1974) and both he and Joe want to follow in their famous father Fenton Hardy's footsteps as detectives. When the father of one of their school friends is wrongly accused of stealing, the Hardy boys take it upon themselves to clear his name and solve the mystery.
After Frank and Joe solve their first case, Fenton—although he had not wanted his sons to get into the detective business because of the dangers involved—starts asking for their help on some of his cases.
Fenton and his boys working together play a bigger part in this series than in any of the following Hardy Boys series.
In this series, Frank is in the same grade as Joe (who is a year younger), because he lost a year due to sickness, but in all the other series he is a grade ahead of Joe and him losing a year is never mentioned.
Casefiles
In the Casefiles, the differences between Frank and Joe are more pronounced as Joe's personality is somewhat changed because of the death of his girlfriend, Iola Morton. Frank (although the death of Iola does affect him somewhat) stays more or less the same.
In the Casefiles series, the Hardy boys collaborate with The Gray Man, who works for the Network—a secret government intelligence agency—to fight the Assassins, an international terrorist organization responsible for his girlfriend Iola's death.
Also, the Casefiles were written between the late 1980s and 1990s unlike the original series (1927–79), home computers were available, and because of this Frank's character is modernized and he becomes a PC computer buff; in one book he is even able to hack into the Bayport City computer system. Frank is also well-versed in the making of bombs and is also able to disassemble them, which saves his and many other's lives many times. As was the case in the previous series, Joe acts as the mechanic for the boys and is often described as being very athletic.
Super Mysteries
This was a series of 36 paperback novels in which the Hardy Boys teamed up with intelligent young female sleuth Nancy Drew.
One character arc seen throughout the series is the mutual attraction between Nancy and Frank. The couple shared a kiss twice in the series; the first in book 5, The Last Resort, when the two are trapped after an avalanche and fear that they will die. The second is in Secrets of the Nile, where they kiss on a balcony after the case is solved. However, the kiss is interrupted by Bess Marvin. Another hint at their relationship is when Nancy's longtime love interest Ned Nickerson saves her. However, a disheveled Nancy calls out Frank's name instead, believing him to be her saviour, and severely disheartening Ned.
The two decide not to pursue relationships, believing that they belong with their current partners, Ned Nickerson, and Callie Shaw. Both partners are jealous of the time and bond shared by the detectives, especially shown in Ned Nickerson. He greatly disapproves of Nancy's sleuthing in the series, as well as the time she spends solving them with the Hardys.
Another romance is hinted at between Joe Hardy and Bess Marvin, although there is much less evidence of this attraction. Neither relationship was ever given a final closure.
Undercover Brothers
In this series, Frank and Joe are both undercover agents for American Teens Against Crime (ATAC), an organization founded by Fenton Hardy.
This is the first series in which Frank and Joe are regularly single (not dating Callie Shaw and Iola Morton, as they did in the previous series), and have different love interests from book to book. Frank becomes nervous around teenage girls, even though they are attracted to him more in this series than any other. In contrast, Joe, in a similar manner to his personality in the Casefiles series, is a huge flirt; however, unlike in Casefiles, girls are relatively less interested in him, preferring Frank, which greatly annoys and frustrates Joe. The brothers use a more modernized speech style, and frequently tease and get on each other's nerves; nonetheless, they are still very close and protective of each other as in all of the previous series.