If you're dressing as a movie or TV character, chances are your costume will need a wig. So many characters have their own distinctive hairstyles. There are a lot of great costumes inspired by the movies and TV, and many of them are vastly improved by changing your look with a wig. Characters from fantasy and science fiction often have very unusual looks. A wig may be essential for achieving that character's appearance. You can't be Gandalf without long white hair, you can't be Jacob without short, spiked, black hair, and you can't be a Na'vi without long black braids. In many cases, these wigs are not even optional if you want to look like those characters.
Many shows and films are full of characters with stylized hair. Think the Brady Bunch women. or the characters in Grease or The Rocky Horror Picture Show. Many times a wig will make you more recognizable than the costume. Characters from The Addams Family or The Jersey Shore can be identified by their hair as much as by their outfits. Disney movies have provided their share of characteristic hairstyles. Ariel's bright red hair stands out, as does Rapunzel's long, long blonde locks. And don't forget Cruella De Vil's black and white spikes.