Greg appears as a plump middle-aged man with a dark-beige beard surrounding his mouth. Greg has taupe hair styled in a mullet that goes down to his waist, with a large bald spot on the top of his head. He usually wears a white tank top, with long or short gray pants or jeans. He has a tan line on his shoulders and feet (possibly from a shirt and pants he wore before). He also occasionally wears a black t-shirt or a green sweater. Greg's skin color is a peachy red color, with the tan line spots being a light apricot color. He wears teal flip-flops, although he tends to go barefoot or wear other kinds of footwear.
Greg seems to be an overall kind person living a simpler lifestyle. He is known to be friendly and genuine, and, so far, has retained an honest attitude concerning his feelings as an individual. He appears to be easy-going and an optimist; his catchphrase is "If every porkchop were perfect, we wouldn't have hot dogs". While Greg is not necessarily knowledgeable about many of the situations he faces, he often tries to give the best advice he can that is based on his own experiences, which can have much value in their simplicity and his pragmatic view on things.
Much like his son, Greg cares deeply for his loved ones and friends, such as when he went out of his way to get closer to Rose despite the boundaries between their species. He is similarly characterized as paranoid of the worst happening to Steven, which stresses him to no end. Despite this, he tries his best to put on a brave face for his son with the knowledge that it made Steven happy and fulfilled, as seen in "Entirely New".
Greg was born under the DeMayo name, and grew up wanting to be a rock star. Eventually, he started to persue this dream of his, and became a rock star after dropping out of college, under the manajor Marty. Apparently the relationship wasn't good, since he considers Marty "dead to him". The exact details on how he met Rose Quartz is currently unknown, Rose eventually gave up her physical form to give birth to Steven. In Steven's younger years, Greg took care of raising Steven until he could move in with the Crystal Gems and learn to use his powers. Greg has since settled down in Beach City, where he lives in his van and owns a local car wash, supporting Steven with his income.
In "Grounded to Earth", Greg was shown what involvement the Gems had in making the Galactic Ray, but upon learning that Steven Universe was going with them, he flat out refuses to allow it and "grounded" him, in terms of keeping him to Earth rather than fully punishing him. He didn't allow Steven to leave the planet until "Preparation" after Discord explained how safe he actually was.
In "Out of Dodge", Greg invites Amethyst to a rock concert to her excitement. Later, he arrives, and tells Amethyst that he will not be able to go with her due to a previous request from Barb to play cards with her and Vidalia. Barb threatened to hold his mail if he did not, and according to him, she is not a "woman of empty threats".
In "New Chaos In Town", Buck Dewey and Lars Barriga found him working in the car wash when he was confronted by Grootslang. Grootslang said Steven told him a lot about Greg, including how little he was involved with him lately, Greg stating that the Crystal Gems didn't want him involved at all. He was left wondering if he should visit Steven, feeling guilty for it.
When the Beach City Flooding occurred, he allowed the Frymans a stay inside his van until their homes were built.
In "To Give or Not To Give", he arrived to the Barn House with his son and the Mane Six after Rhodonite managed to contact them as a stranger arrived at their home. Greg revealed that he is Andy DeMayo, introducing him as his cousin. After learning of Steven being his nephew, he blames Greg for not telling him, his only retort being that he hadn't seen him in years. He went back to the Crystal Temple, being blamed for the situation by Rhodonite for not telling them about Andy in the first place. After that, he made it known that Andy was not the type to change his mind so quickly. He returned to the Barn and was asked about who the "wife" was out of the Gems, him telling Andy that Rose was no longer with them. He aided the group in the upcoming dinner, hoping that it would properly change his mind on letting the Off-Colors stay.