Not much is known about his past, except that he went to the Pandora Kingdom to get the Pandora key so the Federation could achieve its goal.
It is unknown when Clover met Cyan, but Shadow ended up staying with him when a promise was made: He’d get the three magical crystals of the staff of Kairos, and Shadow’s sister Rose would wake up.
Clover failed to get the key due to Joker, Queen, Spade, and young Silver Heart stopping him. During a fight with the three phantom thieves and one agent, Clover got his arm shot off and almost died. He was, however, saved by his present day self.
Sometime before the series, (when Clover was called Professor Clover) he alongside Doubt disguised himself as Joker’s deceased parents in order to steal the Time Telling Goddess statue that was in Joker’s mansion.
Around the time Clover met Joker, he also met Diamond Queen and Shadow Joker. In the anime, he met Queen when she was visiting her parent’s grave, and lied to her that Silver Heart was the one who killed her parents. He then let her stay with him with the promise that she would be able to get her revenge on the phantom thieves. In the manga, he did not meet Queen in her past, and Queen found out about what happened to her parents when looking through some old papers.