Did your ancestor fight in the Napoleonic wars?
Look for him in muster rolls but don’t always assume the first person you find with his name is actually him! Usually, however, if two soldiers in the regiment had the same name, the parish where each was born will be noted alongside his name which will help you identify your man.
The General Service Medal, awarded retrospectively, by Queen Victoria in 1847, was issued with “bars” naming the battles a man had taken part in. Listed on the medal rolls, they’ll tell you much about his service.
Waterloo veterans often became local celebrities. It’s worth double-checking for them in the local press.
Their tombstone may also reveal some interesting details about their life and death.