The Doctor's two true loves. Both women reflect who the Doctor was and what he needed during his respective generations. War torn, the Ninth (and Tenth) Doctor needed Rose to show them what mercy, and even love, looked like. As for Eleven, he needed a strong and bold woman to offset his feigned simplicity. That's where River came in.
The Man who ran away and his box...down through the years.
...Or to make it even more confusing the doctor's daughter who played the doctor's daughter and is also the doctor's wife who went to school with the doctor's daughter going back in time to flirt with King Arthur, who just so happens to have a manservant/sorcerer best friend who once took a journey with the doctor on a ship over a planet called Midnight