When Old Longfellow was much younger, he was in a romantic relationship with a woman named Hannah. One day when they went to meet up at their usual spot, members of the Church of Atom jumped the pair - severely wounding Longfellow and taking Hannah away. It took him two months to recover from the injuries he received, but when he found Hannah, she had already been converted and was now a follower of their ways. Later, Longfellow discovered Hannah was pregnant with his child, but the radiation she worshiped had caused her to have a miscarriage. This is one reason that Old Longfellow hates the Church of Atom.
Old Longfellow is first met at the Last Plank and lives on his own in a cabin near Far Harbor. He has a reputation for being an experienced hunter and an expert in moving about the fog, often escorting people through it - however, most of his escorts end up dead as they often underestimate the fog and its dangers.
Longfellow is a heavy drinker, often asking if the Sole Survivor can stop for a drink or, when trading, if he can be provided with alcohol.
Despite the fog driving most people insane (such as the Trappers), Longfellow seems to be quite sane and reasonable—though he often claims his limbs are stiff and his bones ache due to the exposure of the fog.
Longfellow openly dislikes the Children of Atom; disliking if the Sole Survivor joins them and when talking with DiMA when he talks about the possibility of there being peace with them, he openly states he would enjoy fighting them. Interestingly, he disapproves if the Sole Survivor suggests to spare or reason with Sister Gwyneth when talking to Grand Zealot Richter in The Heretic mission. This is possibly he dislikes sparing a Child of Atom, even if that is the order of another Child of Atom.
When Idolized, he will reveal he always wanted a son and/or daughter to teach what he has learned to them.
He will become hostile if Far Harbor is destroyed.
He is not resistant against radiation.
He will sometimes sing the traditional Irish songs "Wild Rover," "Molly Malone," and "Jug of Punch" when idle.
Sometime when picking up junk items, he will jokingly question why you'd need something 3 times older than himself. Since by the events of Far Harbor took place 210 years after the Great War, which would be around the same time the last of most pre-war junk was made, that would put Old Longfellow at around 70 years old.
While utilizing power armor does not negatively affect Old Longfellow's opinion of the player character as it does for Strong, he will state he's not overly fond of powered armor because "It's too damn loud to hunt in".
The following is based on unverified behind the scenes information and has not been confirmed by canon sources.
Old Longfellow may be a reference to the Maine-born poet Henry Wadsworth Longfellow, whose appearance was similar. The real Longfellow died in Cambridge, Massachusetts, and also had a wife who suffered a miscarriage.
End of information based on unverified behind the scenes information.