Dr. Onésimo Hernández Lerma, a graduate of the Higher School of Physics and Mathematics (ESFM), is currently a researcher at the Center for Research and Advanced Studies (Cinvestav), both part of the National Polytechnic Institute (IPN). He has dedicated more than four decades to the study of stochastic control, a branch of mathematics that enables decision-making in uncertain scenarios. His work has had an impact on fields such as economics, engineering, and systems theory, establishing him as a key figure in mathematical research in Mexico. He is also one of the world’s leading mathematicians in his field, as evidenced by the high number of citations his work has accumulated.

Over coffee and in a relaxed tone, Hernández Lerma even jokes about how “difficult” the questions prepared by Conversus News Agency (AIC) are, Hernández Lerma begins a conversation that, more than an interview, becomes a window into a life dedicated to mathematical thought. His story does not begin with a clear calling, but with an unexpected turn marked by the country’s historical context.

“I was studying physics… and I got caught up in the 1968 student movement,” he recalled. That movement forced him to interrupt his studies on hold and stay home for months. It was during that confinement that something decisive happened: he began studying mathematics on his own. “When we returned to school, I went back to mathematics, not physics,” he said, as though describing a simple decision that would ultimately shape his entire career.

That moment marked not only a change in career but the beginning of a path that would lead him to become one of the leading figures in stochastic control in Mexico. He explained that this field studies systems involving chance, where not everything can be predicted with exact precision. “These are systems that depend on chance, on things one cannot predict immediately, such as when an earthquake will occur,” he noted.

Far from the abstract nature that many associate with mathematics, his field of study has concrete applications—ranging from controlling an epidemic to deciding how to invest resources in economics or how to optimize processes in engineering. “Control theory is about controlling systems to achieve a specific goal,” he explained.

His approach to this field was not planned. After finishing his degree, he began teaching at the Higher School of Mechanical and Electrical Engineering (ESIME), Zacatenco Campus, where his contact with engineers led him to take an interest in practical applications. “Everyone was talking about control and communications, and it caught my attention,” he recalled. That is how he found a combination that would define his work in applied mathematics.

Throughout his career, Hernández Lerma has developed models that enable decision-making under conditions of uncertainty. Among his most cited works are optimal control models, Markov decision theory, and several articles on stochastic processes that are now essential references in the international literature. However, when asked about his most important contribution, he shies away from any spotlight. “The truth is, I’ve never really thought about that kind of thing; you just keep working and things gradually emerge,” he said with a humility that contrasts with the scope of his work.

That same attitude comes through when he talks about the impact of his research. Although his work has been cited for decades, he prefers not to dwell on it. “I no longer feel the need to keep track of who cites me; I hear when a colleague mentions my name, but I don’t think about those things,” he said.

Since he was named Emeritus Researcher in the National System of Researchers and Research Fellows (SNII) in 2014—and previously at Cinvestav in 2009—he stopped worrying about that constant monitoring.

His influence is evident. He receives messages from students and researchers from all over the world. “Scientists from Belgium, Colombia… write to me, ‘Hey professor, I read that you did such-and-such,’” he noted. Sometimes, the requests are so basic that his response is straightforward: “Just look it up on Wikipedia,” he recalls with a laugh, highlighting both the accessibility of knowledge and the enduring relevance of his name in the academic community. For him, citations remain a way to measure impact. “It’s a way to gauge researchers’ influence,” he said. And although he avoids quantifying it, he acknowledges that his work is still actively used. “I know it’s been significant because I receive correspondence daily and see that my work is still being used.” Much of that global recognition stems from texts that are now classics, such as Discrete-Time Markov Control Processes, Numerical Methods for Controlled Markov Chains, or Learning and Approximation in Stochastic Systems, works that have guided generations of mathematicians and control specialists.

His legacy is also reflected in the training of new generations. He has supervised 24 doctoral theses and continues to work with students today. Some of his former students are now professors and researchers. “Two professors here in the department are my former students,” he mentioned casually, as if it were a natural consequence of time.

However, their relationship with them is not constant. “That doesn’t mean we’re in constant communication, but when an opportunity arises, we consult with one another,” he said. It is an academic network that, rather than being formal, stays alive through the occasional exchange of ideas.

When discussing the current state of mathematical research in Mexico, he highlights the growing interest in the discipline. More universities, more graduate programs, and a greater presence of Mexicans in scientific publications. “Thirty years ago, it was extremely rare, though now it’s very common to find Mexicans,” he stated.

His message to young people is optimistic. He challenges the idea that mathematics is difficult. “I found it very simple because it’s very logical,” he explained. In his view, the problem isn’t complexity, but prejudice. “If they took the trouble to understand it a little, they’d see that it’s the most natural thing in the world,” he noted.

That clarity is also reflected in his understanding of knowledge; in mathematics, there are no gray areas. “It’s either true or false—there’s no such thing as ‘half-true,’” he said, contrasting it with other disciplines where interpretation plays a greater role.

Even on a personal level, he maintains an honest view of himself. When asked about a “superpower,” he doesn’t speak of genius, but rather of a limitation: his memory. “I’ve had a bad memory, but I know where to find things,” he remarked. That phrase encapsulates his approach: it is not about knowing everything, but about knowing how to arrive at knowledge.

In the end, when asked to summarize his legacy in a single sentence, he doesn’t mention theories or academic achievements. His answer is simple and down-to-earth: simply “being persistent”, and he added that “if you work hard, something has to come of it.”

That idea runs through his entire story. From the lockdown that led him to discover mathematics, to the articles that are still cited decades later, his career is not defined by spectacular moments, but by sustained discipline over time. In a field where chance is the subject of study, the life of Onésimo Hernández Lerma seems to show that even in the unpredictable, there is room for logic, hard work, and persistence. Because, as he plainly puts it, in the end everything comes down to working and letting the results emerge.