Dir command question...

Why with 'dir' existing in /usr/bin as a program coming from the Gnu coreutils, is there also an alias aliasing 'dir' to "ls -l"??? "alias dir='ls -l'" is in the alias list... with the coreutils, surely the alias is surplus to requirements??? Also, how can it be removed from the aliases? technical question... If I were to type 'dir', which would actually get executed??? the alias to the ls -l command or the 'dir' program?