During his childhood, Jonathan was proud and mischievous, yet gentle. Despite already aspiring to be a "true gentleman",[1] Jonathan lacked manners and mostly behaved like a normal child. His mother having died before he could remember her, and his fellow boys ostracizing him because of his status left Jonathan somewhat lonely.[2] While at first, Jonathan didn't have his future strength of will, Dio unwittingly because of the catalyst of his growth by pushing him to the edge and humiliating his then-girlfriend Erina Pendleton.[3] However, he did have the kindness and courage to immediately jump to Erina's rescue against two bullies bigger than him despite not knowing her.[1]

First and foremost, Jonathan strives to become a "true gentleman." He carries his Joestar name with pride, never betraying the code of conduct he has set for himself and will treat any fellow human with respect unless they prove evil.

Jonathan also possesses a fierce inner strength and the drive to face and overcome conflict, which Dio calls an "explosive power". That drive, fueled by his affection to his friends and loved ones, enabled him to overcome the direst situations, notably managing to save his wife Erina when their boat was overcome with zombies and he was fatally hit in the throat.[4] Jonathan fights for what he believes in, and once he is committed to something, he won't back down until the deed is done. During his journey to find a cure for his father's illness, he was ambushed by a band of misfit hoodlums. He did not so much as flinch as he grasped an assailant's knife within his hand, saying he had much more riding on the fight than merely four fingers.[5]

As a gentleman, Jonathan is also kind and positive. Jonathan has a mindset where he tries to imagine the consequences his actions would have on other people, even if they appear to be enemies.[6] He is gentle and sympathetic, feeling pain even as he vanquishes a zombified copper. Despite his skill in fighting, he will never seriously harm a person without a valid reason. Even after everything Dio has done, Jonathan still considers him his brother, and sheds tears for him.[7] His courteous nature as well as his mental fortitude and ability to withstand fear and pain, is the main reason Speedwagon decides to aid him on his journey. During his life, Jonathan has always had an impulse to save others, beginning with Erina, and ending with his thought of a nearby baby just as he was agonizing from Dio's attack.[8]

Yet Jonathan can feel righteous fury at the evilness of his foes, and will conduct justice by vanquishing them. He admitted that his reason for fighting Dio wasn't out of duty for saving the world, but to avenge his loved ones Dio killed.[9] Moreover, he has no pity for truly despicable individuals he is not familiar with such as Doobie.[10] 

With his courage and spirit, Jonathan sets a legacy as the first JoJo of the series.

Fascinated with the Stone Mask, Jonathan tried to study it and even took on the path of archeology.[11] However, not having thought of putting in on anyone, Jonathan didn't discover its true purpose himself.