The John Doe of the British army. In the 1800s The Duke of Wellington provided the name Thomas Atkins as a label for the common soldier, based on the name an old soldier he once knew. It was consequentially used as a generic name on War Office forms, and eventually it caught on as a name for any old army Joe.
It was latter shortened to the more familiar Tommy Atkins, and often only to Tommy. This Thomas Atkins was the Tommy referred to in Rudyard Kipling's famous poem of the same name.
During WWII Thomas Atkins was used as a name for any unknown soldier.