What he use to be.
He use to be Colonel Jonathan O'Neill. SG-1s bravest man, most trusted, universe's number one good guy.
But that was before.
He would travel the galaxy with his trusty team, freeing the people from their slavery to a false god, making it a happy day.
His funny yet dumb jokes would lighten the mood of any situation, even when they faced death, he could say the stupid little things that made them laugh.
He was the leader of the closest team, and sometime he wish he was closer (to Sam), he would always be there for them and they for him.
He was a strong man, but not just physically, mentally also. You had to be for his job, or you would fall apart.
But that was befor the mission. The one that went all wrong. The one he wasn't there for his team. He doesn't really talk about it, actually he never talks. Now he is another person.
Now he sits, starring out the window. He has shut everyone and everything out. A strong, worthy hero now a crippled old man.
No gleam in his eye for his 2IC, just a tear of lost love. No need to get out and 'Kick some alien ass'. No need to do anything, not even live.
I guess he is no longer the famous Jack of Stargate Command,
Just an empty shell for his memories.