Charles Babbage's Difference Engine was said to have influenced the modern computer as we know it today. It was the first of its kind; a calculating mechanism capable of a precision of up to 20 decimal places. At the time, the people tasked with working out these advanced sums (and occasionally getting answers wrong) were called 'Computers', which is a rather interesting notion - in comparison to what we think of when we hear 'computer' today.
The Difference Engine paved the way for machine automated calculation, and (later on) electronic processing; things that humans can do, but machinery is better, and far more efficient at doing.