Any novel you write is likely to have multiple characters. Most will have a name, but what do they look like? It saves a lot of trouble and time once you’re writing if you plan the descriptions in advance. Some authors even go though magazines and catalogs to cut out pictures of faces they can describe in their story.
Does the character have any other skills, education, weaknesses, or fears that will be an important part of the plot? You should plan those things well in advance, too.
Remember, those are also traits you need to introduce into the story several chapters before they become important. For example, you can’t surprise your readers with the hero suddenly speaking French if you haven’t mentioned it earlier. Likewise, it will seem very contrived if the heroine is cornered in an alley by four bad guys and proceeds to take them all out with her outstanding martial arts or her superb shooting skills if the audience hasn’t been clued into those skills, or the fact she carries a gun, well before the incident. In The Blizzard, we know the hero has a reason to be in the woods on the fateful day and also possesses some prowess in woodsmanship because those facts were introduced earlier.
An author friend of mine copied the following list from a podcast he watched on creative writing from the University of Warwick. You may find such an outline helpful.
Relation to other characters:
Where he lives:
With whom he lives:
Is he happy:
Why or why not:
Reason for nickname: