Hilary is Mordecai's mother. She is a minor character who first appeared in "The Thanksgiving Special".
Not much is known about Mordecai's parents, except that they have been married for 25 years ( "Maxin' and Relaxin'") and that Mordecai is their only son. During Thanksgiving Dinner, they visited Mordecai at the Park and had a lovely time; later CJ and Mordecai come to their house for dinner.
Hilary is constantly embarrassing her son (unintentionally) by taping Mordecai's most embarrassing moments (which she calls Mordy Moments). Mordecai is terrified that CJ will leave him after meeting his mother, to the point that he asks his dad to get her out of the house so they can stop by and pick up a mix-tape. His dad doesn't follow through with his son's request (as he hasn't told a lie to her in 25 years of marriage) and Mordecai spends the evening being mean to his mom, asking her to be "normal".
Mordecai finally realizes that his actions aren't justified and that he should just enjoy the Mordy Moments as it's the embarrassing things in life that make us who we are.
When they were getting the groceries out, they saw the park rising up into Space to which they worriedly saw their son was in the dome.
In the series finale, William and Hillary ran through the crowd hugging Mordecai and Hillary kissed Mordecai on the cheek.
Hilary appears to like jogging and keeping fit. As she does "punchercize" class regularly. She is also shown in "Sad Sax" riding a fitness bike while she gives Mordecai advice on how to win CJ back after he kissed Margaret under mistletoe at a Christmas party in "Merry Christmas Mordecai".
Hilary is a female blue jay who resembles her son Mordecai. However, unlike her son, she does not have white stripes on her arms or blue feathers anywhere on her head. She has blonde hair and wears a wedding ring.
Her appearance changes between the episodes she appears in: in "The Thanksgiving Special", she has neck-length blonde hair and wears a long orange dress with a pearl necklace.
In "Maxin' and Relaxin'", her hair-style has changed and she wears a salmon-colored shirt and white pants, and there are no blue feathers on her head. When she does fitness or "punchercize" she wears a pink singlet, purple track suit pants, pink sneakers, and she also wears sweatbands on her arms and a white and magenta strap on her head. She wears them in both "Maxin' and Relaxin'" briefly and in "Sad Sax".
- Hilary has two voice actors, Jennifer Hale voiced her in "The Thanksgiving Special", and Katey Sagal voiced her in "Maxin' and Relaxin'" onwards.
- It is debatable how far Mordecai's parents actually live: during The Thanksgiving Special, they apparently needed to take a plane to the city where the park is, but in "Maxin' and Relaxin", it appears to be within driving distance. Possibly this means they move out of the first house that appears during The Thanksgiving Special to the new one shown in Maxin' and Relaxin'.
- Although It is speculated that Mordecai's parents moved houses, the house is the same in Mordecai's flashbacks.
- Despite Mordecai having blue "hair" like a typical blue jay, his parents have human like blonde and brown hair.
- Mordecai's mom appears to work out normally as shown in Maxin' and Relaxin', and Sad Sax.
- William and Hilary both share the same first name of former President and First Lady William and Hilary Clinton, respectively.
- According to Calvin Wong, Mordecai's mother is named "Hilary". She's named after Hilary Florido, a former storyboard artist on the show and now the storyboard artist on "Steven Universe".