This is the first JoJo: Jonathan Joestar. We can see from this illustration that Jonathan looks glaringly similar to a certain guy called Kenshiro. This dude here also packs a punch in the series due to the fact that he was one of the few characters who defeated Dio outright and slaughtered vampires (Jotaro got lucky IMO).
The second JoJo (and the best one in my opinion): Joseph Joestar. This dude here is beyond awesome! He fights like none other in the shonen genre and does absurd yet amazing things during fights and even when he's old and senile he still has a kick or two left in em. Not to mention that he is the ONLY character to use both Hamon and a Stand at the same time.
The third and silent JoJo: Jotaro Kujo. The grandson of Joseph through Suzie Q, he is the one person who can break his limits by getting REALLY REALLY pissed at his enemy. He first activated Star Platinum's time stop ability when he was pissed at Dio. Also one of the more popular JoJos in that he appears in four parts of the manga and also has both video games and OVAs that revolve around his portion in the story. He even got an honourable mention in Heroes by Hiro:)
The fourth JoJo: Josuke Higashikata AKA. Hamburger head (Josuke: I'll kill you for that!!). His stand powers sound simple but is actually one of the most versatile stands in the series. Also known as the illegitimate son of Joseph (that asshole :) ) which ironically makes him the uncle of Jotaro despite Jotaro being older than him.
The fifth JoJo (or rather, GioGio): Giorno Giovanna, also known as Haruno Shiobana. While he is not truly a member of the Joestar family, his father Dio Brando impregnated his mother while he was in Jonathan's body, thus making him (technically) the direct son of Jonathan. He is IMO overpowered! The guy is literally untouchable once his stand is upgraded. Hell his dad wasn't this powerful.
The sixth JoJo: Jolyne Kujo. Her dad is none other than Jotaro, and she stands out as being the only FEMALE JoJo in the series as of now. Fun fact about Jolyne: she was apparently the inspiration behind Juri's design in SSFIV :)
The seventh JoJo: Johnny Joestar. He is the parallel universe version of Jonathan. While they are they technically the same, their personalities and way around people are totally different. He starts out as a sidekick to a certain character which I won't name here, but gradually shows growth and becomes a full fledged MC.
The eighth and current JoJo: Josuke Higashikata (JoJolion version). Not much is known about him except for the fact that he has four balls (as in testicles).