Depends on what point in his life....
My dad has always been an amateur military historian, and avid collector. He's gone through phases in his primary interests, however. When I was really little, he had an impressive collection of German WWII firearms, uniforms and insignia. I have vivid memories of his den being lined with dozens of Lugers, P-38's and Mausers. He had a .22 Mauser trainer that I learned to shoot on. He also had an MP-40 that I got to shoot once.
When he lost interest in the German stuff, he went though his 1911 phase. This was my middle school years. He had all the WWII variations (except Singer, of course), lots of pre-WWII, etc. He built shadow boxes with 1911A1's displayed next to letters, photos and mementoes of the actual soldiers who carried them (provenance meant a lot to him).
Then he went through a Michigan State Police phase (we lived in Michigan at the time, and my father worked with the MSP). He sold off his 1911 collection and built an impressive collection of firearms used by the MSP through the years.
Finally, he got interested in the Civil War, and that's been his focus for the last decade or so. He's got quite a collection of Spencer rifles, Colt cnb revolvers, etc. As usual, he's primarily interested in the history behind them, so he thoroughly researches the units each was used by and puts together elaborate historical displays for them. He volunteers as a guide at two different museums in the Atlanta area, and puts on living history demonstrations with repro Spencer and Henry rifles.
