Throughout the series, Steven ages from a child into a teenager, growing to about 5'6". He is recognized by his signature thick, dark brown curly hair and optimistic nature. As a pacifist, his core philosophy is rooted in empathy, love, and diplomacy, though he frequently struggles with the immense expectations and complex legacy left behind by his mother. Steven Universe is the only known human-Gem hybrid, born to the Crystal Gems' former leader, Rose Quartz, and human musician Greg Universe. He is kind-hearted, empathetic, and initially possesses his mother's pink diamond in his navel, which fuels his vast array of magical abilities.

Pearl projects a tall, slender humanoid form with a pale complexion and a conical hairstyle. Her namesake gemstone is embedded in her forehead, which she uses to summon a magical spear, project holographic images, and store weapons or items. She possesses highly refined talents in fencing, ballet, and engineering. Intelligent and meticulously organized, Pearl often acts as the strategist of the Crystal Gems. She grapples with deep-seated insecurity and lingering grief from the loss of Steven's mother, Rose Quartz—whom she deeply loved. Over the course of the series, her character arc focuses on overcoming her past trauma and realizing her own self-worth and independence apart from serving others.

Garnet is composed of Ruby (a hot-headed, passionate fighter) and Sapphire (a calm, clairvoyant aristocrat). Their fusion is incredibly stable and serves as an emotional anchor for the rest of the team. As the de facto leader, Garnet is known for her level-headedness, though she has grown to be a more communicative and flexible mentor to Steven compared to her early, aloof days. Garnet has three eyes; the top violet eye allows her to calculate probable futures, letting her anticipate enemy attacks and plot the best course of action.

While Garnet and Pearl act as structured guardians, Amethyst is the "cool aunt" or sibling of the group. She is loud, carefree, and proudly embraces human culture—especially food and television. Beneath her rebellious and comic exterior lies a vulnerable "sad clown" dealing with intense imposter syndrome and abandonment issues stemming from her creation in a forced Homeworld project. As a quartz gem, Amethyst boasts superhuman strength, enhanced agility, and the ability to heal from almost any injury by retreating into her gemstone.

Originally an uptight, techno-centric perfectionist who views others as inferiors, she evolves into a passionate, quirky Earth defender known for her blunt honesty and catchphrase, "You clod!". She is highly skilled in engineering and mechanics. While she initially relies on clunky technological "Limb Enhancers" for flight, energy blasts, and interfaces, she later learns she possesses innate ferrokinesis (the ability to control metal). Introduced as an overseer of the planet-destroying Cluster, she gets stranded on Earth. After forming a truce with Steven, she officially joins the Crystal Gems in "Message Received" by defying Yellow Diamond and goes on to become a key protector of her new home.

Lapis Lazuli is a powerful, tragic, and fan-favorite character in Steven Universe. Known for her signature brilliant blue hair and water wings, she possesses unmatched hydrokinesis. Her character arc follows a profound evolution from an isolated trauma survivor seeking escape to a loyal, heroic protector of Earth. She has striking blue skin, dark cobalt hair, and navy-blue eyes. Her gemstone, a tear-shaped, deep-blue Lapis Lazuli, is embedded in the center of her upper back. Instead of summoning a traditional weapon, Lapis projects brilliant, translucent, glowing wings of water from her gemstone, allowing her to fly at incredible speeds. She has vast control over water, allowing her to create clones, form massive constructs, walk on water, and even drain entire oceans. Lapis was originally a Homeworld Gem whose primary function was terraforming planets. During the Gem War, she was mistakenly "poofed" and trapped inside a magic mirror for thousands of years. Freed by Steven, she was deeply distrustful of the Crystal Gems, later enduring immense trauma through forced fusion (as seen with her toxic fusion into Malachite)

Jasper is a ruthless, powerful Homeworld Gem soldier created on Earth's Beta Kindergarten. Originally serving Pink Diamond and later Yellow Diamond, she is characterized by her muscular build, orange-and-red striped skin, and prominent gemstone located on her nose, which she uses to summon a crash helmet. Jasper is a tall, muscular Gem with light tangerine skin and darker orange-brown stripes. She has thick, flowing, off-white/beige spiky hair and dark brown and red Homeworld attire featuring a yellow diamond emblem. Her gem is situated exactly where her nose should be. initially considers fusion a "cheap tactic to make weak Gems stronger," a sentiment she holds against the Crystal Gems. However, her desperate desire to win eventually drives her to use fusion and even corrupting herself to gain more power.