Sebastian is Alonso’s brother and one of the men who is shipwrecked on Prospero’s island. He is callous and impressionable, and he plays henchman to Antonio’s villain. He is an instantly dislikable character from the moment we meet him. For example, he is cantankerous and unhelpful during the shipwreck in 1.1, and he shows a clear lack of empathy in 2.2 when he blames the grieving Alonso for Ferdinand’s alleged death. 

As the play progresses, it becomes abundantly clear that Sebastian is as cowardly as he is unkind. Antonio is able to convince Sebastian to kill Alonso and claim his throne, but one gets the sense that Sebastian wouldn’t have acted without external assurance. He also concocts a ridiculous story about lions when he is caught above the sleeping Alonso with his sword drawn to keep himself out of trouble.  

Interestingly, Sebastian’s ambitions are left unresolved by the end of The Tempest. There is no reconciliation between Sebastian and his brother. In fact, there are only vague allusions on Prospero’s end about Antonio and Sebastian’s plot to kill Alonso and place Sebastian on the throne. This has caused many to question the stability of the text’s happy ending. After all, the play ends with Alonso heading back to Italy on a ship with his would-be-assassins.