JoJo

JoJo (ジョジョ) is a nickname shared by each of the main protagonists of JoJo's Bizarre Adventure, derived from the recurrence of "Jo" in their names.

In the text of the manga during Part 1 and Part 2, it is used most frequently in reference to Jonathan and Joseph Joestar.

 Each of the protagonists is also descended from the Joestar Family, and as such all bear the Joestar Birthmark.

Non-Protagonists
The following characters are not protagonists in the series, and some do not even belong to the Joestar bloodline. However, it's notable that their names are able to be shortened as "JoJo":
 * Geo rge Joe star I (ジョージ・ジョースター)
 * Geo rge Joe star II (ジョージ・ジョースター 2世)
 * Holy  Joe star-Ku jo  (in the context of her maiden surname and husband's surname)
 * Sada o Ku jo (空条 貞夫)
 * Shizuka Joe star (静・ジョースター)
 *  Geo rge  Joe star I
 *  Geo rge  Joe star II
 * Norisuke Higashikata IV (born  Josuke )
 *  Jo sefumi Ku jo
 * Kūjō Sadafumi (空条 貞文)
 *  Joe  Ku jo 

Origin
Araki admits that the idea for the name came from his neighborhood's local Jonathan's restaurant where he and his editor would often hold midnight meetings. The two decided the protagonist's first name would be Jonathan, and Araki, using Steven Spielberg's name as a reference, decided the last name should follow the same format, and thus Joestar was decided. (Steven Spielberg's name in Japanese is スティーブン・スピルバーグ, or "SUtiiben SUpirubaagu" - thus the SuSu/JoJo format) Araki mentions that it was risky using this type of name, as using a foreign name for a main protagonist at the time was considered taboo.

Araki also admits that stories such as East of Eden and the TV series Roots inspired him to use a periodical style where the main character changes, but the story continues; although this was not a very Jump-style format for manga at the time.