I need to preface this by admitting I've only read the first two-thirds of 'Colossus: The Fire Dragon', but I found the key characters to be kind of a mixed bag. The obvious one is Roland, the chronicler—he's our point-of-view character trying to document the supposedly extinct fire dragons. I liked him well enough, a bit naive but earnest.
Honestly, the actual 'key' character, for me, was the Colossus itself, the ancient fire dragon. The book spends so much time building up this mythic presence through ruins and legends before it even appears. That felt more central than some of the human cast.
Roland's guide, Elara, was crucial for the journey's logistics but her motivations felt thinly sketched until the very end. There's also Lord Vane, the patron funding the expedition, who clearly has his own agenda. The dynamics between those three drove most of the plot, even if the dragon stole every scene it was in.