J. F. (John Frederick) Foster

Best known as the author of Three Months of My Life, he was an assistant surgeon in Her Majesty’s 36th Foot. The diary was published after his death in 1873 and presented as the journal of the late J. F. Foster, edited by Lizzie A. Freeth.

Sources available during this search agree that he was born in 1839 and died in 1869. They also describe him spending part of the summer of 1868 in Kashmir for health reasons, where he kept notes that later became his book.

Firm biographical detail beyond that is limited in the material I could confirm. What stands out instead is the tone of his writing: observant, modest, and immediate, with the feel of a private record that happened to preserve a striking historical journey.