The Atanasoff-Berry Computer, or ABC, is in many respects the first electronic digital computer. It was conceived in 1937 by Iowa State College (now Iowa State University) physics professor John Atanasoff (October 4, 1903 – June 15, 1995) and built with the assistance of graduate student Clifford Berry. It was completed in 1941.
Although Atanasoff filed for a patent for his computer, when the U.S. entered World War II, Atanasoff left Iowa State College and the patent process was not completed. A court case, Honeywell v. Sperry Rand, determined that the patent for the well-known ENIAC (Electronic Numerical Integrator and Computer) was invalid because many of the ideas derived from the Atanasoff-Berry Computer. The ruling was released October 19, 1973.
The Atanasoff-Berry Computer had to be re-programmed before each task, so it is arguable whether it was truly the first modern computer. It is clear, however, that it was a stepping stone in the development of ENIAC.
In some respects, the Atanasoff-Berry Computer was more advanced than ENIAC: It was binary and employed parallel computing.
Further information on Atanasoff's life and work can be found in a downloadable article, John Vincent Atanasoff: His place in the history of computer logic and technology, by Irving H. Anellis.
There's a new book that sheds some light on Atanasoff and the computing device he invented:
The Man Who Invented the Computer: The Biography of John Atanasoff, Digital Pioneer by Pulitzer Prize-winning author Jane Smiley.
A synopsis of this book can be found on National Public Radio.