Miles (Hey Arnold!)

Miles (Phil and Gertrude's only child) was a scientist/doctor who visited remote parts of the world to help people who didn't have access to medical help. He didn't have much of a love life, as he felt that no woman would put up with all of the travel he had to go through, until he met someone who not only put up with travel but did quite a bit of it herself - a doctor/botanist named Stella. However, two or three years after his son Arnold was born, they had to fly one more mission - and they haven't been heard from since.