Final answer:
The speaker of the lines is Macbeth, who expresses his guilt and lack of peace despite having achieved the title of king.
Step-by-step explanation:
The speaker in the lines 'We have risked everything, our name, our future, and our souls to murder, but we've not gained the peace and happiness that being king and queen would suggest, since we're so guilty' from Shakespeare's Macbeth is Macbeth himself.
These lines express Macbeth's realization that despite achieving the highest status of king, the peace and happiness he and Lady Macbeth expected to enjoy are overshadowed by the guilt and fear resulting from their heinous actions; primarily, the murder of King Duncan. This expression of guilt is one of the play's central themes, showcasing the psychological turmoil that results from wrongdoing, especially when done in the pursuit of power.