For each of the following characters of A Midsummer Night's Dream, describe them as a character and the effect they have on the outcome of the play...

Egeus is Hermia’s father.  He wants her to marry Demetrius, but she is more interested in Lysander.  Egeus brings Hermia before Theseus, who rules that she has to do what her father wants, under Athenian law.

THESEUS

What say you, Hermia? be advised fair maid:
To you your father should be as a god;
One that composed your beauties, yea, and one
To whom you are but as a form in wax
By him imprinted and within his power
To leave the figure or disfigure it.
Demetrius is a worthy gentleman. (Act 1, Scene 1) 

Hermia’s reaction to this is that Lysander is also a worthy gentleman.  Hermia’s role in the play is as a sort of protagonist, making Egeus a kind of antagonist.  If Hermia had not refused to marry Demetrius and run off with Lysander, the four young people would never have been in the woods for all of the mischief that ensues.  Ultimately, Hermia is able to wed her choice when Theseus overrules Egeus. 

Helena is another antagonist for Hermia, because she wants to marry Demetrius.  Normally, this would not be a problem since Hermia is not interested.  However, Helena does not believe her. She tells Demetrius that Hermia and Lysander and eloping, and they both end up following the couple into the woods.  Helena is fiery, self-centered, and persistent.  When the lovers are anointed by Puck and both men end up chasing Hermia, Helena is beside herself with rage and grief.  Fortunately, she ends up with Demetrius so there is a happy ending. 

Titania and Oberon are the fairy queen and king.  They are fighting over Titania’s changeling.  Titania is so upset that the forest seems to have turned to winter.  Oberon and Titania are significant, because their presence causes the confusion in the woods.  Oberon has Puck anoint Titania’s eyes as well, so that she falls in love with Bottom, the craftsman practicing a play in the woods.  At the time he is wearing an ass’s head, so he is an even more hideous choice.  Oberon is making a fool of her to get back at her.  When the spell is off, she leaves bottom and goes back to Oberon.

Oberon and Titania’s role in the plot is to cause mischief and humor through Puck, and to present another view of love.  They are older, and their argument and making up demonstrates love’s complexity.  The fact that they make up adds to the play's happy ending.