Don (Physical Attraction... Chemical Reaction)

Don is the father of Brian.

History
Don came to the hospital when his son, Brian, swallowed a marble. George O'Malley examined him and said the marble would pass on its own, so they just had to wait. The marble passed that night, but they came back to the hospital the next day because Brian was having extreme abdominal pain. He swallowed what he thought were eight marbles, but were actually magnets. He had to be rushed into surgery to remove them and repair the damage.

After surgery, Jane was told Brian would be okay. She said that she and Don used to have a great relationship, but then things happened and she said maybe them taking a break was a good idea.

Romantic
He is married to Jane. They used to have a great relationship, but things had strained it and they fought all the time. After Brian's surgery, Jane admitted that maybe them being apart was for the best.

Familial
His son, Brian, made himself sick in order to get his parents to take him seriously when he asked for them to get divorced.

Career
Him losing his job when Brian was little contributed to his marital problems.