the role of bosla in duches of malfi ?

Bosola is the tool through which the Cardinal and Ferdinand perpetrate most of their evil in The Duchess of Malfi. He is hired by Ferdinand to spy on the Duchess, for whom he serves as manager of her horses. He is an enigmatic figure, willing to murder for hire without hesitation, while initially reluctant to the commit to the seemingly less extreme vice of spying.

As his deeds lead to worse and worse consequences--the banishment of the Duchess and her family, the murder of the Duchess and her children, Antonio’s accidental death--he shows more and more remorse for his actions. It is only when Ferdinand and the Cardinal refuse to reward him for all he has done, though, that he stops blindly following their orders, and avenges the Duchess and Antonio by murdering the Cardinal and Ferdinand.