HOW TO CRAFT THE ONE-DIMENSIONAL CHARACTER
One-dimensional characters (1DC) are great tools to use if you are trying to highlight a specific trait in your other characters. Say for instance you want show what your hero is not like (i.e. prideful and boisterous).
One tool to use would be to create a 1DC who is prideful and boisterous. Your 1DC will radiate those two traits so vividly that any pride that your main character has will be overshadowed by the 1DC. There are so many avenues that 1DCs can take, and they really do not need to have much backstory or definition. A few simple explanations will suffice.