“Fortinbras” means 'strong of arm', which is very significant in understanding the character. The website “everything2” provides a succinct discussion of the role of Fortinbras in Hamlet, laying the groundwork for an excellent comparison / contrast essay:
“Wherever Hamlet irresolute, Fortinbras is 'strong of arm'. ... Hamlet has lost his father; Fortinbras has lost his father. Hamlet seeks vengeance; Fortinbras seeks vengeance. The difference? Hamlet whines, bemoans his existence, sulks, sneaks. Fortinbras cleverly and swiftly invades Denmark, reclaiming his father's lands and restoring order. . . . Fortinbras is a leader with clear ambitions; Hamlet, is paralyzed by his madness. And as the restorer of order, Fortinbras does what Hamlet could never do. And perhaps most significantly, Fortinbras acts decisively and lives whereas Hamlet's fiasco results in a divided kingdom and his own death in addition to the death of many others. In some ways, this makes Fortinbras the incarnation of a critique of Hamlet's tragic flaw.” This last comment, which I put in bold, seems a particularly useful view of Fortinbras.
I would add that Fortinbras introduces one of the first (it might be THE first) revenge plots in the play. Horatio describes that Fortinbras seeks revenge on Denmark because his father King Fortinbras lost land and later his life as the result of a battle with King Hamlet. This gives the play something of a "historical" context for the revenge them which will run rampant throughout the play. This context serves to foreshadow the mood of the play as well as the climactic invasion of Elsinore in Act Five.
Hamlet uses fortinbras as a pawn in his quest to make claudius believe that he has gone mad in grieving for his father. It looks like a camel... Due to fortinbra's gulible nature he falls and believes that hamlet is mad due to his love for Ophelia