In the 1930s, Elsie the Cow was the logo for Borden dairy products.  The company had a live cow named Elsie for personal appearances.  There was so much demand for Elsie that Borden had to find another cow to make appearances, too.  They found a bull instead, named him Elmer, and call him Elsie's "husband."

Borden's chemical division originally wanted to use Elsie as "spokescow" for their new white glue.  But the dairy division didn't want Elsie to be associated with a nonfood product (especially one that looked like milk).  So, they decided to use Elsie's husband... and called it Elmer's Glue-All.