There’s supposedly only one person who can call him Lucas — but others do.
On season two, episode eight, “The Ins & Outs of Inns,” Mia, the owner of the Independence Inn where Lorelai works, comes to town.
She greets Luke with a hug and calls him Lucas, to which he responds, “You’re the only person in the world who can call me that.”
But later, on season five, when Luke takes Lorelai to Sniffy’s Tavern, the owner, Maisy, also calls him Lucas.
Maisy went to high school with Luke’s mother, so he’s known her even longer than Mia.