[p_l]

Pascal had two killer apps.

First, it was used for teaching, like Java today. So you had a wide base of programmers knowing it.

Second, there was Turbo Pascal which made it an extremely popular language on PC platform (also used to have significant presence on Mac, but I'm less familiar there.

[askvictor]

Three: Delphi. Programming has never been as fun as with Delphi.

[reikonomusha]

Pascal was also used to program Mac OS.

[EamonnMR]

Classic MacOS, it should be noted, not the recent rebranding of OSX.