Who conceived the concept of Discrete Event Simulation, and when?
Cornell's Conway, Johnson and Maxwell's paper Some Problems in Digital Systems Simulation, was published in 1959 in Management Science.  It discusses many of the key points of a discrete event simulation, including managing the event list (they call it an element-clock) and refer to "more efficient but more complicated methods" for locating the next event, but don't discuss the heap data structure.  This paper refers to earlier publications, but they don't seem to discuss the specifics of a discrete-event simulation like this paper does.