Queen Gertrude, Hamlet’s mother, had a lot to deal with, not the least of which is her seeming mad son Hamlet speaking to ghosts in her own bedchamber.  

HAMLET

How is it with you, lady? 

GERTRUDE  

Alas, how is’t with you,
That you do bend your eye on vacancy
And with the incorporal air do hold discourse?
Forth at your eyes your spirits wildly peep;
And, as the sleeping soldiers in the alarm,
Your bedded hair, like life in excrements,
Starts up, and stands on end. O gentle son,
Upon the heat and flame of thy distemper
Sprinkle cool patience. Whereon do you look? 

HAMLET

On him, on him! Look you, how pale he glares!
His form and cause conjoin’d, preaching to stones,
Would make them capable. Do not look upon me;
Lest with this piteous action you convert
My stern effects: then what I have to do
Will want true colour; tears perchance for blood.

Gertrude

To whom do you speak this?

—Hamlet, Act 3, Scene iv

Ah, ‘that you do bend your eye on vacancy…’   What a lovely line. In so many ways, Gertrude’s little speech is the whole great play writ small. Who was Gertrude, though? Shakespeare never reveals much about her. What’s really important is how Hamlet sees her, and the view through that lens is dark and twisted.

Was Gertrude an adulteress? Complicit in her husband’s murder? Incestuous because she married her dead husband’s brother? All of these accusations are Hamlet’s suspicions, but a close reading of the lines of the play (in all of their various versions) doesn’t conclusively affirm any of these accusations.

I believe Gertrude was an innocent, doing what she had to do for her Kingdom (that is, marry Claudius after her husband the King had died). Her innocence parallels Ophelia’s innocence. They are the only two female speaking roles in the play: and neither are treated well by Hamlet. But can we blame Hamlet? The evil done to his father–like most evils perpetrated in this world–are seeds sown, spreading calamity (which brings to mind a great line by Hamlet in another scene, ‘Tis an unweeded garden That grows to seed.’ King Claudius’ evil act jaundiced Hamlet’s view of the world and, I believe, how he saw his mother.

The image is of the great Glenn Close from the 1990 version of Hamlet, an excellent version I think, and very much worth a view. Here she is kissing her son, Hamlet (Mel Gibson) flirting with the various incestuous memes running through this stupendous play.