Dr. Alex Richards joined the NCR Army sometime prior to the first battle over the Hoover Dam between Caesar's Legion and the New California Republic. He served in that battle as a medic, and was present for some of the worst of the fighting- and the gruesome aftermath it left behind. Richards considers himself- and anyone else who was in that battle- lucky to be alive, but nonetheless stayed on and continued to serve in the Mojave.
As events began shaping up for a second battle for the Hoover Dam, Richards was stationed at Camp Forlorn Hope, the sole surgeon, doctor and medical expert of any kind at the camp's medical center. As the Legion captured the town of Nelson, immediately to the south, and put Camp Forlorn Hope under a grim state of siege, Richards quickly found himself overworked and his talents needed more and more often. Seeing men he managed to help and or even save from death go right back to the front lines- all too often to be injured again or killed- wore away the last of Richards' idealistic motivation for joining the NCR Army, making him weary and demoralized. Richards never once discusses quitting, however, and works as hard as he can to deal with the casualties that are brought to his tent.
Richards originally joined the NCR Army out of idealism; he believed in what the NCR and its army stood for, and wanted to go somewhere that he could use his talents and make a difference. After seeing so many men die and be injured or maimed- often, seemingly, for no reason at all- Richards has given up on such high-minded ideas and now grimly sets about his work, wanting only for the fighting to end.
If one has the Confirmed Bachelor perk, Dr. Richards will address the player character as "little buttercup," "[my] fine dear," say "I'm always a sucker for a pretty face" or exclaim that the room just got a little bit hotter, indicating that he is homosexual. This is confirmed if the player character has the Wild Wasteland perk, as a name in the credits reads "Dr. Richards is a dude, and he likes dudes."