Like Hamlet, Laertes and Fortinbras are sons confronted with a father's death. To what extent do they function as foils to Hamlet?
In Hamlet, Fortinbras, Hamlet, and Laertes all have experienced and reacted against the death of their fathers. Yet, while they are all three fatherless, their reactions to patricide differ, as is natural for those of such varying temperaments. Hamlet, of course, experiences a turbulence of emotion, ranging from absolute rage and the desire to avenge his father's death to melancholic procrastination. Fortinbras, about whom the audience learns little, vows to reclaim the lands that were once Norway's and is willing to risk his life for "an eggshell," and Laertes seems impetuous, at best, as he peremptorily reaches an accord with the nefarious King Claudius to murder Hamlet for the death of his father when he himself has been eager to depart from him. Thus, of the three, the noble Fortinbras is the most unselfish, with Laertes as the least unselfish.
That Laertes has inherited some of his father's self-serving proclivities is suggested in Ophelia's response to his advice to her.
....But, good my brother,
Do not, as some ungracious pastors do,
Show me the steep and thorny way to heaven,
Whilst, like a puff'd and reckless libertine,
Himself the primrose path of dalliance treads
And recks not his own rede. (1.3.49-54)
But, like his fawning father, Laertes allows himself to be exploited by Claudius, who engages him as a henchman while deluded Laertes believes that Claudius aids him in avenging himself against Hamlet. In the end, the dying Laertes begs Hamlet's forgiveness as he has hit him against his conscience. "I am justly killed with my own treachery" (5.2.286). Further, he confesses,
The foul practice
Hath turned itself on me. (5.2.292-293)
Laertes serves as a foil who is impetuous, rather than dilatory, judgmental rather than deliberate and pensive. Yet, he does display some nobility in the end, a nobility worthy of some respect. By contrast, Fortinbras acts quickly, but his swift actions are much more honorable than those of Laertes, actions which complement, rather than contrast with, those of Hamlet.