The name Tommy Atkins, used to describe the typical British soldier, probably originated in a War Office publication of 1815. This pamphlet showed how a Soldier's Book should be made out, and gave Pte Thomas Atkins as its example. Some have suggested that the Duke of Wellington suggested the name himself, in memory of a soldier in his regiment who had been killed in Flanders in 1794. The nickname had wide currency by the 1880s, and was universal in World War One.
Source: http://www.bbc.co.uk/history/lj/warslj/army_04.shtml