Trujillo is the dictator of the Dominican Republic. He functions several ways in the book: he is the impersonal head of a repressive state, but he is also a character who interacts personally with Minerva and her family.

Ultimately, what Trujillo does is have the Mirabal sisters murdered. But before that, we learn of his many crimes. For instance, as a girl, Minerva learns from Sinita that Trujillo's "secret" is that he "is having everyone killed"—knowledge that begins her radicalization. Later, Trujillo shows up in person at her school, attracted by her beautiful classmate Lina. Lina eventually becomes one of Trujillo's many mistresses. Minerva learns about this fate one day on a trip to the capital, when her father casually points out the gated mansion where Lina lives.

Minerva comes to understand that Trujillo stands for a specific kind of sexual violence against women. This becomes all too clear when Minerva actually meets Trujillo at a party. Trujillo is sexually attracted to Minerva, but when he gropes her during a dance she slaps his face. Minerva's defiance of Trujillo's sexual advances leads to her father's imprisonment and a personal interview with Trujillo, in which Minerva has to bargain for her father's freedom. In this sense, Trujillo represents the brutality and misogyny of macho culture.

What  is Trujillo's motivation in In the Time of the Butterflies?

Trujillo, as befits his role of dictator of this novel, has but one motivation: to do everything he can to sustain and continue his autocratic regime that allows him to do anything he wants and to maintain an iron fist of control over the population of the Dominican Republic. Throughout the novel, Trujillo is presented as a figure who knows what he wants and whose will is only matched by that of the will of Minerva, as she imagines after she gambles for her future:

I look down at the lopsided scales as he puts his dice back. For a moment, I imagine them evenly balanced, his will on one side, mine on the other.

However, it is clear that Trujillo is not used to meeting people who stand up to him, as he has his pick of women and expects even the wives of his officials to sleep with him, as Minerva realises when she goes to the banquet at el Jefe's residence:

Under the tablecloth, a hand is exploring the inner folds of a woman's thigh. I work it out and realise it is Trujillo's hand fondling the senator's wife.

The motivation of Trujillo is therefore to do whatever he needs to do in order to sustain his power and continue in the kind of unchallenged position he occupies where he can do anything he wants without consequences. It is of course this motivation that the Mirabel sisters are willing to die to oppose.