G'lant is Zanna and David's Valentine dragon. As David lay dying on the Arctic ice, in Zanna's arms, he placed a gift into her palm, calling it his Valentine dragon. The name G'lant was sent to Zanna by way of Gadzooks, David's special writing dragon. This was revealed at the end of Fire Star, hinting that David was still alive. At the beginning of The Fire Eternal, Zanna gives G'Lant to Alexa because she could not "care for him any more"
In The Fire Eternal, it is shown that G'lant may not have been imaginary and David might have created an actual dragon - though Arthur hints that David may have been somehow "transformed" and that G'lant is his chosen name for his new self. G'lant is invisible to everyone, even those who can see dragons, except Alexa, who can see and even draw him (even though it might be her imagination).
In Dark Fire, on Scuffenbury Hill, the Ix & darklings were fighting David and Grockle. David stepped in front of Grockle, and his eyes turned purple. David morphed into Grockle to create the Fain i:lumminis known as G'lant.