Gnarrk is a Neanderthal and a Honorary Titan, along with his friend and partner Kole.
The exact background of Gnarrk is unknown, though he is revealed to have been exposed to the modern world once before. This left him with a severe technophobia which remained with him until his meeting with the Teen Titans. Kole and Gnarrk eventually teamed up and retreated into a subterranean prehistoric world still populated by dinosaurs, where they have remained ever since. Gnarrk can understand English but is unable to speak it.
Kole and Gnarrk met the Titans upon their attempt to apprehend Doctor Light, who had built a light collecting and amplifying machine to harness the power of the Arctic auroras. In short succession, Doctor Light and the Titans crashed through the ice on the surface and found themselves in another world. The Titans were immediately beset by a pack of raptors, from which Kole and Gnarrk rescued them. After introductions were made, Kole invited the Titans for dinner; during this, Cyborg got a little too friendly with Kole, prompting Gnarrk's jealousy. Gnarrk finally stormed out after Cyborg beat him at an eating contest.
Soon after, Kole followed Gnarrk and reassured him that he's still her best friend and she'll never leave his side. Immediately afterwards, Kole was kidnapped by Doctor Light, who intended to use her crystal-based powers to run his machine. Gnarrk teamed up with the Titans and followed them to the surface, where he, in face of Kole's plight, overcame both his innate fear of the surface world and his technophobia and aided the Titans bringing down the villain. For their assistance, Gnarrk and Kole were made Honorary Titans.
Soon afterwards, the Brotherhood of Evil set their plans in motion to capture young heroes around the world, and Kole and Gnarrk were fought Gizmo and Billy Numerous. Despite overwhelming odds they managed to hold their ground, and later joined Cyborg in the final assault against the Brotherhood's base. They are seen taking down Ding Dong Daddy by smashing his car. Later on, they were in Titans Tower socializing with the other Titans, and later assisting them in preparing to capture Doctor Light once more.
As a Neanderthal, and also because of his bad experiences with the modern world, Gnarrk has a limited educational horizon. He is however, quite adaptable and can rise to any challenge, especially where Kole is involved. It is apparent that he values Kole more than just a friend and partner (it is unclear whether this feeling is reciprocated on Kole's part), and therefore he gets quite jealous and overly protective if someone gets too close to her.
Though he is capable of understanding English, his vocabulary is extremely limited, consisting only of the word "gnarrk". Still, Kole is able to understand and communicate with him perfectly.