Mr. Mortman is the name of the librarian, introduced in The Girl Who Cried Monster.
Summary[]
Lucy leaves her skates at the library, so she returns after closing hours to retrieve them. She then sees him eating bugs and then turning into an ugly, orange monster. She then leaves. The next day she stays after closing and takes a picture of him as a monster. But then he sees the flash and spots Lucy and chases her all the way to her house. But at her house he gives her her backpack she left back at the library. Later while Lucy and her family are at the gas station Mr. Mortman spots Lucy and helps her pick up some pictures. Then Lucy's family invites him over for dinner. At dinner, Lucy's mom and dad turn out to be monsters too, who devour Mr. Mortman.