Rutherford "Gus" Aris (September 15, 1929 – November 2, 2005) was a chemical engineer, control theorist, applied mathematician, and a regents professor emeritus of chemical engineering at the University of Minnesota (1958–2005).

Aris was born in Bournemouth, England, to Algernon Aris and Janet (Elford). From a young age, Aris was interested in chemistry. Aris's father owned a photo-finishing works, where he would experiment with chemicals and reactions. He attended St Martin's, a small local kindergarten and moved to St Wulfran's, a local preparatory school, now Queen Elizabeth's School. Here, he studied Latin (a skill he would make much use of later in his life) and was encouraged to continue pursuing his interest in chemistry. Because of his achievements, he was referred to the Reverend C. B. Canning, Headmaster of Canford School, a well-known public school, close to Wimborne. On the strength of this interview, he was given a place in the newly created house that the school had provided for day-boarders. This was in 1943, when he was 14. His mathematics teacher, H. E. Piggott, had a particular influence on Aris due to "the liveliness, enthusiasm, and care that he brought to his teaching", which "were unparalleled in my experience". Piggot spent substantial time on pure and applied mathematical papers, an experience that Aris described as "extraordinary". Aris dedicated his book Discrete Dynamic Programming to Piggot 15 years later.

Piggot helped Aris to get a job working for Imperial Chemical Industries (ICI) as a laboratory technician in the Mechanical Engineering Department of the Research Labs, at the age of 17. While working at ICI, Aris attended the University of London part-time to work toward his B.Sc. Aris described this as "an excellent way to get a degree, although perhaps not so good a way of getting an education." After 2 years Aris made an attempt to earn the B.Sc. Honours Degree. He sat 12 papers (exams) covering a wide range of mathematical topics, and got a degree with first-class honours.

In 1948, ICI sent him to Edinburgh, Scotland for two years of study at the Mathematical Institute at the University of Edinburgh, which was presided over by Alexander Aitken. Aris, who was accepted for post-graduate studies but not for a Ph.D., did post-graduate work at the University under the supervision of John Cossar. During this break from ICI, Aris also registered for a University of London M.Sc. in the area of mathematical analysis. When he sat the papers, however, he failed to get the degree.

In 1950, Aris returned to ICI and began working for C. H. Bosanquet in Billingham, England. Working with Bosanquet provided Aris the opportunity to work on a large variety of problems, including catalysis, heat transfer, gas scrubbing, and centrifuge design.

Aris was then promoted to Technical Officer, where he began working on chromatography. He utilized results from a paper on dispersion written by Geoffrey Taylor, and extended its results, ultimately writing a paper in 1955 that applied the method of moments to Taylor's approach. He submitted the paper to the Proceedings of the Royal Society, with help from Taylor (who was a Fellow of the Royal Society). Aris communicated with Taylor regarding dispersion and diffusion. In the meantime, however, he was transferred to a different division, where he began working on chemical reactor design. Frustrated with the transfer and with the proprietary nature of his commercial work, which made publishing work very difficult, he decided to move to a university, applying for several lectureship positions during 1954 and 1955 without success. Aris continued to work at ICI, focusing much of his efforts on mathematical modeling of adiabatic multi-bed reactors, a topic that was the central focus of an M.S. student at the University of Minnesota. In 1955, Neal Amundson of the University of Minnesota, who was on sabbatical at Cambridge, visited the ICI Research Department, where Aris was working. Amundson suggested to ICI, during his visit, that Aris be sent to the University of Minnesota in Minneapolis for a year of study. Several months later, Aris later met Amundson at Cambridge and told Amundson of his plans to leave ICI for academia, plans that he had not revealed to his superiors at ICI. Amundson offered Aris a research fellowship at the University of Minnesota, which Aris accepted. After notifying ICI of his intent to leave, he moved to Minneapolis, Minnesota at the end of 1955.

Aris began working on chemically reacting laminar flow, applying Kummer's hypergeometric function to the problem, and control of a stirred tank reactor with some unusual properties. Both problems required the use of a computer to perform calculations, and Amundson provided Aris with a computer science graduate student with whom to work. Aris's research fellowship was extended for a second year, but shortly afterward, in October 1956, Aris was informed of a lectureship opening at the University of Edinburgh. He took advantage of the opportunity, and left immediately for Edinburgh.

Aris was on the faculty of the University of Edinburgh for two years, 1956–1958. While at Edinburgh, Aris wrote papers on his work at the University of Minnesota and at ICI. Having the lectureship position allowed Aris to gain experience lecturing to students. He also attended the lectures of, and interacted with, the chair of chemical technology at the University of Edinburgh, Kenneth Denbigh, who was a well-known thermodynamicist and an editor of the journal Chemical Engineering Science.