Custom Dolls are dolls that have been customized into unique looks or characters that American Girl has not made.
This can include (but is not limited to) custom Historical Characters, modern dolls, and characters from other literature, movies, or media.
Reasons for Customization
A highly popular reason for custom Historical Characters is that American Girl will probably never be able to cover every time period in the history of the United States. The company has skipped over some significant periods such as the Late Victorian Era from the 1870s to the early 1900s and Civil Rights Movements of the 1950s-60s. Also, it is highly unlikely that a doll will be created in a time period before Kaya'aton'my, as she is billed as the First American Girl. Custom characters can be created for these times that American Girl will most likely not cover or have not covered.
Historical periods that have been covered have not been covered from all possible angles, especially angles that can be considered controversial such as race and class (most Historical Characters are middle to upper class at some point in their series, or basic working class). Also, some people may enjoy the fashions and items from a time period, but not the character or the aspects shown by said character. In these cases they may wish to make a Historical Character of their own that covers that time period.
While American Girl has created Best Friends for some Historical Characters, they have not done every Best Friend yet (and will not with the discontinuation of the line). Furthermore, some characters have what can be considered "multiple" best friends. For example, Molly McIntire's best friends in the stories are Susan Shapiro and Linda Rinaldi; however, Emily Bennett was chosen to be her companion.
Released dolls may also not be what a person is looking for; sometimes American Girl has modified the characters image. (The most striking is Elizabeth Cole, who was changed from a brunette to a blonde; a more minor difference can be seen with Ruthie Smithens, who was given grey eyes.)
American Girl will probably never release a male character, not counting the Bitty Twins line. However, the dolls are very gender-neutral in shape for a prepubescent child. Custom male characters have been made from the dolls and are generally dressed in a more masculine fashion.
Given the very nature and marketing of the My American Girl line (in that the dolls are nameless and purchasers are encouraged to create their own characters), they can be modified into any character, and many purchasers and collectors use the dolls as a base to create custom dolls.
Some people, rather than restoring a damaged doll to original looks--which often necessitates sending in to an American Girl Hospital and the cost of repairs and restoration--choose to customize a doll. This is a more labor intensive, but possibly cheaper method. Furthermore, to avoid identical looks a person may customize two alike dolls.
Methods of Customization
Clothes changing and/or modified hair styles are the easiest and most prolific method of making a custom doll. This requires nothing more than changing the clothes and hairstyle a doll wears. Doll modification allows for more drastic changes, such as rewigging.
Through American Girl, dolls without hair or with hearing aids are available. These--along with earrings--are the only modifications that are done by the company and will not prevent a doll from repairs.
At the most complex and permanent, people have dyed the vinyl and bodies of dolls to a different skin tone. This can only be done with light-skinned dolls; darker dolls cannot be bleached lighter.
Customizing and the American Girl Hospital
Heavily customized or modified dolls will not be repaired by American Girl, such as those with eye swaps or rewigging.