I'm so psyched for lonesome road and anxious to see what the courier's background and a lot of people make their own stories so here is mine.
Born in the divide, the courier lived in a little shack that when he was 18, it got raided by Caesar's legion lead by one named Ulysses. The courier and his father tried to fend them off but lead to the courier's father getting sliced and stabbed to death and the courier having to find cover until it was over.
After the wave of legionaries, The courier tracked Ulysses to his camp where he killed all the recruits, trainers, and veterans to get to him. The courier was very low on ammo for his 9mm pistol, but he didn't care, Ulysses shot the courier's arm and got away while the wounded man tried to shoot him. About 5 hours later, he got up from the dirt, went back to the shack, and got his grandfather's armored vault suit and gun. He left to the Mojave, where he became a courier in hope that he could find Ulysses in his travels.
He had no luck, but he was filled with hope when heard about a delivery order with the parcel being a platinum chip. He found out that Ulysses didn't take the job so he did and plus the pay was good. When he was intercepted by Benny he developed amnesia and thus, started Fallout new vegas.