It was certainly one of the first, and for the most part I think it's generally regarded as the first "real" high level language. But there are a number of other languages that were developed at approximately the same time where you could probably quibble a bit about exactly which one came first. COBOL[1], for example, and some of the predecessors to COBOL, like FLOW-MATIC[2] and ARITH-MATIC[3]. Also, as PaulHoule mentions, there was LISP[4], and then there was IPL[5] which LISP descended from. COMIT[6] also dates back to that general era.