Works out how something is likely to fail before it does, and what to do about it.

Every part has a failure rate, and reliability engineers turn that uncomfortable fact into something you can design around: failure mode and effects analysis before a part is built, statistical models of how long components actually last, and the forensic investigation that finds a genuine root cause after something breaks in service rather than a plausible-sounding guess. The job sits closer to statistics than to any one piece of hardware.
Mechanical, aerospace or industrial engineering, ideally with a reliability or statistics course beyond the core.
Mechanical Engineers · US Bureau of Labor Statistics, Occupational Outlook Handbook, May 2024 wages and 2024–34 projections.
Reliability engineering is not tracked as its own occupation. Most reliability engineers are trained mechanical, aerospace or industrial engineers, so this is the closest published figure, for a much larger population than the specialism itself.
A reliability prediction is a probability, not a guarantee, and when the rare failure happens anyway you are the one explaining why the model did not catch it. Root-cause investigation after a real failure comes with real pressure to find an answer fast, and a wrong answer sends the fix in the wrong direction while the real cause keeps failing.