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Tab Spangler is a veteran of the Marines. He started working at Serenity Ranch after he retired from the military, and his military background shows in his mannerisms: namely, his style of speaking which always sounds like he's giving orders. Spangler's military background also shows in the treatments he administers to his fat camp clients: waking them up by clanging garbage cans and lids; making them run and cracking a whip at them; and tearing them down by forcing them to admit to their own role in their weight gain.
Spangler is in his 40s but no older than 47. When he asked Marge to guess his age and she guessed 47, Spangler got angry and said it hurt when people's guesses were over, or even when they were correct. He didn't specify whether Marge's guess was over or correct.
Spangler is a highly unstable personality, prone to emotional outbursts which lead to his yelling at both people and objects. However, he is quick to back down and apologize after he calms down.
The only family member Spangler mentions is his father, from whom he appears to be estranged. When Spangler showed Bart how his family was faring while he was attending fat camp, he said that they would look for his father if there was time left over.
When Bart attended Serenity Ranch, Spangler put him through the full range of treatments. When Bart cheated, Spangler drove him back to Springfield and showed him the measures his family had to resort to in order to pay for the treatment: converting their home into a youth hostel and taking in German backpackers who constantly humiliated and berated them. Confronted with the true cost of his addiction, Bart kicked his junk food habit and needed no further treatment.
Spangler then announced that the Simpsons still had unused (and non-refundable) treatment time, and ended up taking Homer to Serenity Ranch for treatment. While they were driving, Spangler suggested they stop off at a motel and split a room, even though it was only an hour's drive between Serenity Ranch and Springfield. When Homer asked where he would sleep, Spangler said they could worry about that when they were "standing naked before the bed".
 Behind the Laughter