A computer is a machine that takes information in, is able to manipulate it in some way, and outputs new information. There is no single inventor of the modern computer, although the ideas of British mathematician Alan Turing are considered eminently influential in the field of computing. Mechanical computing devices were in existence in the 1800s (there were even rare devices that could be considered computers in ancient eras), but electronic computers were invented in the 20th century.
Computers are able to make complicated mathematical calculations at an incredible rate of speed. When they operate under the instructions of skilled programmers, computers can accomplish amazing feats. Some high-performance military aircraft wouldn't be able to fly without constant computerized adjustments to flight control surfaces. Computers performed the sequencing of the human genome, let us put spacecraft into orbit, control medical testing equipment, and create the complex visual imagery used in films and video games.
If we only examine these grandiose uses of computers, we overlook how much we rely on them from day to day. Computers let us store vast amounts of information and retrieve a given piece of it almost instantly. Many of the things we take for granted in the world wouldn't function without computers, from cars to power plants to phones.