Ambition is a manifest theme of a play driven by its central character's evil quest for power. For Richard (as for all tyrants), this course is a lonely one. In Act I, scene ii, Richard tells us that he has "no friends to back my suit at all / But the plain devil and dissembling looks" (235-36). Richard, of course, has allies (Buckingham, Catesby) and hirelings (the murders and Tyrell), and he even takes Lady Anne as a wife. But as events show us and Richard himself is plain to admit, he has no relationship to anyone, his mother included: those who stand alongside him are mere tools that are best done away with after their usefulness is gone. Most stunning of all, Richard's ambition alienates him from his own self. Thus, after being visited by the ghosts of his victims in Act V, scene iii, Richard awakens in terror and says:

What do I fear? myself? there's none else by:
Richard loves Richard; that is, I am I.
Is there a murderer here? No. Yes, I am:
Then fly. What, from myself? Great reason why:
Lest I revenge. What, myself upon myself?
Alack. I love myself. Wherefore? for any good
That I myself have done unto myself?
O, no! alas, I rather hate myself
For hateful deeds committed by myself!
I am a villain: yet I lie. I am not.
(V.iii.182-91)

Ambition conjoined with an inherently evil nature cause Richard to embrace the role of villain, but he plays the part so fully that he eventually wreaks havoc on himself.