Mortuary Portrait Mystery

A few years ago, I received an old foldable wooden camera, together with a separate magazine (wooden casing protecting glass negative plates from light). Taking a closer look at this precious gift, I noticed that the magazine still contained a glass negative. Looking at the glass plate through natural light, I could see a mortuary portrait taken years ago (impossible to identify and hard to date); I then ventured into scanning this glass plate to reveal the old, beautifully detailed picture it contained (scroll down for picture below).

Who is this old man? And why was this glass negative kept in this magazine? This will remain a mistery...