National Army Museum

National Army Museum (NAM)

Another, more general, source of information is the National Army Museum in Chelsea. The Museum does have a library relating to more general Army/regimental histories (requiring a reader's ticket). Click on the information link for the answers to many frequently asked questions.

This India List link is about a card index at the National Army Museum, prepared by Major V.C.P.Hodson (who published Hodson’s List of Officers of the Bengal Army).Unlike the published List, these cards hold the details of not just officers of the Bengal presidency, but those of the Bombay presidency Madras presidency etc and included Civil Servants, Officers of Eastindiamen, Chaplains & other clergy, and went on to include a good many people from the post East India Co. period up to and including serving officers of the Second World War.
Note that there is no mention on the National Army Museum’s website regarding these index cards.

For a more comprehensive information on individuals, the best place to start is The National Archives.

If you know your ancestor's regiment, there are many regimental history websites.