[Roy Mars III]

major spoilers

Spoiler:

he married Talisa (Jeyne in the books) breaking his promise to the Freys. If he would have married a Frey daugther like he said he would, he would be alive and the war won instead he makes a terrible choice which leads to his death and his mothers, the loss of the war, and the end of basically any chance the Starks have of coming out of the story well

guy is one of the dumbest characters in the story.

Like Ned he is a great military strategist but an idiot when it comes to the politics of the kingdom