Gladys has red, curly hair, dark green eyes and wears a long purple dress, gold earrings and red Mary Janes.
She has a severe facial tic, which usually appears when Billy is misbehaving, when her authority is challenged, or whenever Grim is present, and has also developed nervous breakdowns. Despite so, Gladys cares deeply for Billy and Harold, although when Harold gets fired for doing something stupid or whenever Billy is really disobeying her or acting up, she does have large outbursts of rage.
She wants Billy to grow up to be a chiropractor, even though she knows that is very unlikely to happen. Gladys is a caring mother, a loving wife and a devoted homemaker.
She suffers from an unnamed mental condition (in her first appearance it's mentioned she must have forgotten her medicine when she claims she saw Grim) and is overprotective of Billy. She fluctuates between these qualities at an unsettling rapidity, if any at all. Her renowned fits of insanity and ferocious mood swings have always been present. She even attacked her husband Harold more than a few times, notably with a chainsaw, frying pan, even with a Scythe and many other dangerous items.
Harold implies that she has schizophrenia during her first appearance, asking if she forgot to take her medicine when she tries to tell Harold about Grim. This was present before she even met Grim. Her relationship to Grim is ambivalent at best. She has never come to terms with the fact that her son's best friend is The Grim Reaper himself - and that he is also living under her roof, watching her TV and eating at her table. She is exceptionally mean to him, and they will always bicker if placed in the same room. There is even an episode about their relationship.
At times, it seems as if Billy has inherited some of his mother's madness and angriness.