Jonathan was the gardener of king (then prince) Leopold and the biological father of Zelena who only appeared in the flashbacks of the episode "Bleeding Through."
Pre-episode
Jonathan works as the gardener at Prince Leopold's castle, at some point he comes into possession of a handkerchief with a royal insignia on it (possibly through stealing) and decides to use it to pose as a prince to woo desperate women into sleeping with him.
Bleeding Through
Drinking at a tavern he notices a barmaid being harassed by drunks and offers he a seat. The woman introduces herself as Cora and tells him that she tries to be more than what she is. Upon realizing that she wishes to move up in the world he purposely drops the royal handkerchief and says he is "Prince Jonathan." He then "proposes" to her with a ring made from straw and tells her that he will be out of town for a few weeks, Cora then offers him upstairs to consumate their "proposal."
Months later Cora finds him at the castle where he reveals his fraud and that he never intended to marry her. She is then hurt and angry at him for taking her virtue and good name but smugly he responds that she practically gave it to him when she thought he was a prince and calls her a Harlot. Cora then reveals that she is pregnant to the shocked Jonathan and demands child support, but he responds by knocking her on the head and running away.
When Cora becomes engaged to Leopold he meets up with her in the gardens and threatens to reveal her pregnancy unless she steals gold and jewels from the royal treasury. Cora agrees and tells him to leave before anyone see's them, which he does. Unfortunately for him, the whole conversation was heard by Princess Eva who then told Leopold and banished Cora from the kingdom.
It is unknown what happened to him after that, but obviously he didn't get any money. Although since he was involved in what would have been theft from the royal treasury it can be assumed that he was held responsible for his crime.
Personality
Jonathan is an utter misogynist, he views women as harlots and gold-diggers who would pounce at the chance to marry a man just for happy living. He uses this as justification to lie and manipulate desperate women into sleeping with him without care about how this may affect them afterwards and seems to also view this as a sort of poetic justice. His is completely selfish and doesn't give a dam about anyone but himself, not the women he has slept with or any children he has fathered with them. perfectly willing to abandon them or ruin their lives unless he gets something from them.