My great-grandfather participated in both WW1 & WW2.
He was an inventor (invented a heating system for ambulances + a new design for tank tracks during WW1, writer, even translated comics books from English to French). To add to that, he even won medals during the Olympic games (in fencing if I recall). He's better known for his boxing activities (he discovered Primo Carnera and was his manager until he "sold" him to US-Italians... My grand-father was living with him in the US in the late 1920/early 1930s, I heard stories so incredible). During WW2, he was a Resistant and got jailed at Fresnes, together with two of his sons.
His pic below
My grand-father was a poet, tapdancer, inventor, etc. He fought and finished in a Stalag (his duty was to sort seized/broken vehicles for the nazis = you can imagine the way he was doing it, he he). He was an athlete (used to do boxing, and he was a tapdancer with my grandmother) and one day a nazi officer fell into water and was about to drown. Since he was an excellent swimmer, he saved his life and received some kind of paper after that. Finally, he escaped from the Stalag and entered the Resistance (his fake name was Jacques Roubaix), and got captured by the Gestapo. He ended up in the basement of where the Ministry of Interior is now located in Paris (torture = waterboarding, etc.). He should have been shot but the fact he save a nazi officer saved him. Back to a Stalag. Once again he escaped and joined again the resistance (was a dispatch rider on a motorcycle since he loved those vehicles, even wrote a poem about them that I still have).
WW1 has been the most deadly in my family (and for the French too = major losses, both civilians + army).