Navy Rear Admiral Grace Hopper is credited with finding the first "bug" in a computer during the days of vacuum tubes.

"On September 9, 1947, a team of computer scientists and engineers reported the world’s first computer bug. Today, software bugs can impact the functioning, safety, and security of computer operating systems. “Debugging” and bug management are important parts of the computer science industry.
This bug, however, was literally a bug. “First actual case of bug being found,” one of the team members wrote in the logbook. The team at Harvard University in Cambridge, Massachusetts, found that their computer, the Mark II, was delivering consistent errors. When they opened the computer’s hardware, they found ... a moth. The trapped insect had helped short out a vacuum tube.
The first-reported computer bug was found by computer-language pioneer Dr. Grace Hopper. She is often given credit for reporting the bug - but at a minimum she was the person who likely made the incident famous."