Both series feature characters with very masculine builds and designs, with Jonathon and Dio having designs heavily inspired by Kenshiro and Shin respectively. Both series are also infamous for having numerous gory scenes on a level not seen in modern Shonen, and are less heavy on providing Shonen tropes than most other series (although that's not to say they're absent from the series).
Hokuto no Ken was one of the main inspirations that made Hirohiko Araki write JoJo, that's why both series share a lot of similarities, both thematically and stylistically. First off, the art styles are quite similar, especially in depicting fights between huge muscular men. The characters are also similar, with Jonathan Joestar being proud, stoic and kind, as well as having a strong sense of justice and an explosive determination, much like Kenshiro. Dio, on the other hand, is physically similar to Shin, although his personality is more similar to Souther, since they both are overly ambitious and want to rule weaker people. The plot of both manga is also quite similar, since they both have the main character fight their sibling in order to fulfill their destinies. read more
Both series contain a headstrong protagonist and an arch rival, who in one way or another ruined their pasts, so now protagonists seek revenge and are trying to find a way to stop them. The atmosphere in both mangas is similar when it comes to battles and will to fight as well as mythological themes.
Both mangas are similar when it comes to mood and action. They are filled with fights, monsters and gore. The storyline is also similar: both feature a protagonist who seeks to defeat a former friend, who has destroyed their life. The antagonists are also quite similar: ambitious men who would betray everyone around them to reach their goals.
Very manly and violent old school manga with a lot of action. Both are about an epic rivalry between the main character and the villain. Also in both manga the villain is very charismatic and beloved by most, until the MC discovers his true evil nature.
Both manga are written by Hirohiko Araki, so they share some elements. They have similar art, as well as heroic protagonists, who use their supernatural abilities to fight strong, evil opponents. Both manga are quite action-packed and violent. The main difference between them is that JoJo is horror, while Baoh is sci-fi.
Both are inspired by Fist of The North Star. Sakigake!! Otokojuku starts off as a gag manga with it quickly transitioning as a battle series with a very good tournament arc. JoJo's Bizarre Adventure is very horror-based but contains the same masculine tone in parts 1-3. If you like one then you'll more than likely enjoy the other.
Manly men doing manly things. Both are have a somewhat similar aesthetic (for example character designs and line work), gory fights and both draw quite a bit of inspiration from Fist of the North Star.
Jojo's Bizarre Adventure: Phantom Blood and Devilman are extremely similar story wise, both being about a young boy and their defiant friend finding out about a mysterious mask which will grant a person with a supernatural power, then later haven grown up, the main characters will have to deal with the consequences brought by the powers of the mask.
Both of these manga fall under the same demographic. They feature a main protagonist who fights against supernatural creatures (vampires in JoJo, demons in Devilman). They also contain a lot of gore and violence.
Both manga serve as origin stories for their respective sagas. Also, both explore similar themes, such as destiny, martial arts, lineage, masculinity, and tragedy. Both manga have a lot of action, historical backgrounds, and a combination of realism with fantasy.
While these manga have different genres of horror and science fiction, both series contain characters and events inspired by Fist of The North Star including manly heroics, tragic origins, dying friends, violent battles, and monstrous villains. Lastly, both heroes Jonathan Joestar and Blue follow the belief of enduring tragedies and embracing their kind spirit.
It would seem Hirano Kouta was deeply inspired by Jojo's Bizarre Adventure and perhaps unconsciously managed to grab a few things over to his giant, Hellsing, such as the principles based on which vampires work, posing and even a few scenes. Regardless of these somewhat apparent similarities, the two works are completely different in style and nature.
JoJo's Bizarre Adventure & Kinnikuman are manly series which are still being published today. Both of these manga mark the debut of their current long running status; bearing multiple sequels and spin-offs to their franchise. Kinnikuman is more childish in tone with its wacky character designs but can be dark at violent at times especially when its enemies include satanic figures and corrupt Gods. JoJo's Bizarre Adventure is more horror based but can be as ludicrous as Kinnikuman. Other similarities include: very bizarre events, gritty battles, shonen friendship and the family passage of the next generation of heroes.