WARNING: The following post contains plot spoilers from the movies Iron Man and Iron Man 2.
When I say motivation, what comes to mind in terms of your protagonist?
Many different things can motivate a person or character to action: compassion, anger, greed, desire, envy, or a particular goal.
One of the most effective ways to motivate a major character in your work-in-progress (WIP), however, is with inner demons.
Tony Stark in Iron Man
Viewers meet Tony Stark (played by Robert Downey, Jr.) in the original movie Iron Man. He's a self-described “genius, billionaire, playboy, philanthropist” (albeit in a later Marvel movie). To put it mildly, he's obnoxious, and he doesn't have a whole lot going for him (beyond that critically important sense of self-deprecating humor, which at least makes him marginally likable). He's also making billions of dollars off the production of weapons of mass destruction.
For the duration of the first movie, we don't know why Tony is the way he is. When he takes a different path, moving Stark Industries away from weapons production and in a more humanitarian direction, it's easy to tell what's recently changed. He spent months as a captive of a terrorist organization in the Middle East, tortured and tormented, and he saw his selfless fellow prisoner killed trying to help Tony escape.
Yinsen’s last words to Tony are: “Don't waste your life. Don't waste it.”
When Tony is rescued and returns to the States, he closes down the weapons portion of Stark Industries and takes steps to save people from warfare instead of creating it.
Tony Stark in Iron Man 2
By the second movie in the series, we're really wondering what happened to Tony when he was younger. What is it that drives him to be so successful? To carry on the prestigious name that his father, Howard Stark, made powerful during his own time? To be known for his blase attitude and carefree conquests?
Tony himself provides the answer, with an unexpected diatribe about his father. Everyone has lauded Howard Stark for his efforts and brilliance. Tony's take is surprising: “[He was] cold, calculating. My dad never told me he loved me, never even told me he liked me.”
Now we know. Tony's battling inner demons. He's never felt like enough, so he built a lifestyle around making himself feel like the most important, influential person in his father's business empire.
He's still a little boy, trying to win his father's approval.
What inner demons plague your protagonist? An abusive upbringing, past neglect, unfulfilled desires, a devastating loss, derision by a trusted authority figure … any number of things could be motivating your character's actions in the “now” of your novel. Think through some possibilities.