The first Assembly Language was developed by Kathleen Booth in 1947 for the ARC2 at Birkbeck, University of London following work with John von Neumann and Herman Goldstine at the Institute for Advanced Study. After this several other variations of Assembly Language have been developed and higher abstractions of the language have been created.
Back in the day it was extremely tedious, error prone and time consuming for programmers to "code" in binary. Even the smallest of the tasks required huge amount of thinking and calculations. Building huge programs back then was a mammoth task. So the assembly languages have been created to get rid of. The very tedious part of coding in binary was relieved by assembly and it helped concentrate more on the problems.