Russell's mother and dad are divorced, and that his dad lives with another woman now, and doesn't make the effort to spend a lot, if any, time with Russell, which is why he was so determined to become a Senior Wilderness Explorer as an effort to impress his dad, because when he first talked to Carl on the porch, he mentioned that all the dads would be there(hoping his own would come) at the badge ceremony. But it was a happy ending anyway, since Russell found a father figure in Carl, and Russell ended up being like the child that Carl and Ellie were never able to have.