What is the significance of having Myrtle in the Great Gatsby?

Myrtle was the juxtaposition of Daisy. While Daisy provided him with a wealthy, acceptable social image, she was not much more to him than a mere possession. Myrtle provided Tom to transcend or break social expectations. Tom was so rich; he could wade into any socio-economic situation and use the people he comes into contact with. The filthy rich can touch anything they like as well as destroy anything they like.

Mrytle fulfils a number of roles in the novel. She is a vehicle for Fitzgerald to convey:

a) Tom's callousness. Tom is clearly using Mrytle to satisfy his own ends. Eg, He tells Mrytle that he can't divorce Daisy because Daisy is a Catholic and doesn't believe in divorce (a lie).

b) Tom's brutality. When a drunken Mrytle taunts Tom by repeating Daisy's name... "Making a short deft movemnt, Tom Buchanan broke her nose with his open hand".

Mrytle becomes a key figure in the narrative. When in Chapter 7 she sees the big yellow car approaching she runs out in front of it, the car hits her and she is killed instantly. It is this incident that leads to George (Mrytle's husband) taking Gatsby's life in Chapter 8 of the novel.