Peter the Great made his wife keep her lover's head in a jar after he had him executed.
The Tsar of Russia, Peter the Great, ordered his wife's secretary, Willem Mons, to be executed on charges of embezzlement. Rumor has it that Peter was suspicious that his wife, Catherine, was having an affair with Mons, and thus ordered him to die a particularly gruesome death by drawing and quartering (being hanged, decapitated, and split into four pieces). Mons' head was kept in a jar in the Kunstkamera museum, and Peter forced his wife to spend hours in front of the "exhibit" as punishment.
Ironically, Catherine only knew Willem Mons because his sister Anna was Peter's mistress, which makes Peter kind of a hypocrite.
Peter wasn't any kinder to his first wife, Eudoxia Lopukhina. He used to ignore her and tried to force her to become a nun and move to a convent so she would leave him alone. Then when he found out that she had a new lover, he had that guy executed too (drawing and quartering again). He had her charged with adultery, and even ordered the execution of his own son that he had with her.
In short: Worst. Husband. Ever.