The Indiana-born judge is "a Mexican," Trump has said repeatedly, painting Curiel as a vengeful, intemperate bench presence.
But a simple review of Curiel's public record quickly undermines -- if not outright debunks -- Trump's repeated allegations. And lawmakers from both sides of the aisle, legal experts and civil rights advocates have all denounced Trump's rhetoric.
Curiel himself has remained quiet, his office citing the judicial code of conduct. His brother, Raul Curiel, told CNN: "I know my brother is not taking it seriously. Some other people might ... I think Trump feels that this division is working in his favor but he's actually creating the bigger division as we speak."
Here are five things to know about the federal judge now at the center of GOP standard-bearer's latest round of headline-grabbing attacks.
1. Mexican drug cartel target
Before he was first appointed to a state-level judgeship in 2006, Curiel worked as a federal prosecutor in Southern California with a focus on drug cases -- and with them, the Mexican cartels.
In the late 1990s, Curiel's efforts to extradite a pair of alleged cartel gunmen to Mexico put him directly in the traffickers' crosshairs. The Los Angeles Times reported
at the time that, according court documents, "a top lieutenant in the Arellano Felix drug trafficking cartel" told another inmate he planned to have "Curiel assassinated and that he had requested and received permission from the leaders of the Arellano cartel."
Curiel was quickly provided a security detail, including bodyguards who traveled with him until the threat passed. He would go on to serve, between 1999 and 2002, as the lead attorney for the Organized Crime Drug Enforcement Task Force.
"During this period, he led an investigative unit of more than 20 federal agents and four assistant U.S attorneys that successfully extradited and prosecuted leaders, assassins and members of the infamous Arellano-Felix drug cartel," Sen. Barbara Boxer's office said in a statement following his 2011 nomination to the federal court.
In 2012, Sen. Richard Blumenthal introduced Curiel at his confirmation hearing, touting the judge's "extraordinary experience" and decades in the courtroom.
"One of the most significant cases involved the successful prosecution of the Arellano Felix drug cartel, a multi billion-dollar drug trafficking ring responsible for more than 100 murders in the United States and Mexico," he said.
2. Schwarzenegger's pick
"The judge was appointed by Barack Obama," Trump told supporters during a lengthy San Diego speech on May 27, the day Curiel ordered the release of documents related to the Trump University lawsuit.
But Curiel's journey from prosecutor to the bench began long before President Barack Obama's nomination arrived in November 2011. Then-California Gov. Arnold Schwarzenegger, a Republican, appointed Curiel in 2006
to the state superior court, where he spent six years before ascending to the federal court.
Schwarzenegger affirmed his support for Curiel on Monday tweeting: "Judge Curiel is an American hero who stood up to the Mexican cartels. I was proud to appoint him when I was Gov."
3. Sons of immigrants: Curiel and Trump
"My parents came here from Mexico with a dream of providing their children opportunities," Curiel said in his introduction to the Senate Judiciary Committee in 2012. "And they've been able to do that with the opportunities that this country has to offer."
The future federal judge was born in East Chicago, Indiana, in 1953. His parents, both immigrants from Jalisco, Mexico, were naturalized citizens.
Curiel's brother, Raul, told The New York Times
his father first entered the country as a laborer in Arizona in the 1920s. That would mean Curiel's father was actually in the U.S. before Trump's own mother (she arrived in the 1930s
), who -- like Curiel's -- became a citizen herself after marrying his father.
"My concern is that (Trump's attacks are) hurting other people. It's hurting our image as sons of immigrants. It hurts our people in general," Raul Curiel said in interview with CNN
on Monday. "Being a Hispanic, it hurts these kinds of things. It doesn't hurt me personally. And I don't think it hurts my brother personally. We're above those kinds of things."
4. Indiana, born and raised
Curiel grew up, attended college, and began his professional life in the state of Indiana.
A 1976 graduate of Indiana University, he stayed in Bloomington for law school, entering private practice in Dyer, a city just outside his hometown, three years later. Curiel would spend seven years there, before eventually moving to Monterey, California, to continue his private work in 1986.
He joined the federal prosecutor's office for the Southern District of California in 1989
, eventually being promoted to assistant U.S. attorney in 2002.
5. 'I'm not there to make the law'
Trump has sought to undermine Curiel's propriety by suggesting he could not separate personal politics from the law of the land. But an exchange from the judge's 2012 confirmation hearing
with Sen. Blumenthal, a Connecticut Democrat, suggests Curiel takes a more measured view of his current role.
How did Curiel, Blumenthal asked, "see the role of a district judge versus the appellate court?"
"As a trial judge I recognize that I'm not there to make the law," Curiel said. "I'm not there to interpret the law, I'm there to follow the law as established by the precedent of our Supreme Court."