However the main character is clearly Riggs. Because in trying to deal with his wife's death, he is suicidal. His need is to find a reason to live. For the same reason, there can only be one antagonist or villain who will create obstacles in the path of the main character. By progressively increasing conflict between the main character and the adversary, you will create a story that will sustain the audience's attention and interest.
Conflict is the basis of all drama.
Without conflict, there's no story. If you choose to write a story about a man or woman battling a harsh wilderness environment or any other form of inanimate opposition, it will not work by itself. Only when adversaries act and react through rising human conflict can an audience's attention and interest be sustained. If your main character advances a step towards achieving his or her goal, there must be a setback or counter-thrust delivered by the adversary. This is the primary essence of dramatic writing-one person striving to achieve a goal while another attempts to defeat him or her.