Lt Dan has killed me twice in town. The first time, he attacked me while I was fighting purple priest. Any idea what's going on?

I have had a chat with Dan and told him that it is inappropriate to beat the living daylights out of new players.

He told me he would try to curb his temper and be nicer to new starters and returned souls.

Normally he is a very placid soul.
Generally he will react if attacked and will remember your transgression until either you die or he gets respawned.
I have not heard that he will attack if he sees you attack someone else or other NPCs.

He is listed as a Good NPC, so if you attack him the Peacekeepers will intervene and if you kill him you will lose luck.
He will protect anyone in group 1 ("Guards").

So I wanted a corpse in town for janitor to see so I attacked the purple priest, I saw Lt dan get mad and thought he was coming to beat up the priest with me. But then he just started punching me. :/ He still needs more therapy.

I have respawned Lt Dan.

I suspect he is like the Temple Guards, if he sees you fighting anyone then he will intervene.
This may also apply to skeles in the cursed tomb or any other NPC in the game.

I may even apply to PvP in clans or purple fights.

I have not tested these to see if my suspicions are correct.