The White Baby is an AI and computer virus created by the Amadeus Syndicate. It appears in Metal Slug 4 and Metal Slug Attack.
Metal Slug 4
The White Baby virus was created by Amadeus and used to override the military systems of countries throughout the world via the Internet. In response, the Regular Army dispatched Tarma and Eri to protect the researchers developing a solution for the virus and Marco and Fio, as well as new recruits Trevor and Nadia, to take down the Amadeus Syndicate.
Metal Slug Attack
When the two Rebel Army officers arrived and demanded to know why the Amadeus Syndicate had attacked them, the White Baby appeared and forcibly placed Amadeus in the Mother Computer to fight them. After the Mother Computer was defeated, the White Baby left to find better "toys". Amadeus then explained to Abigail and Allen the origins and purpose of the White Baby.