It's really only fitting to discuss the two main characters from the book of friendship together, since their identities are so totally united. They really only fully come into their own as characters when their friendship emerges. Even then, however, Cambell and Triamond are strangely downplayed on Book 4 of the Faerie Queene.
Even though the title introduces them as our protagonists (although, inexplicably, it refers to Triamond as Telamond—no one knows why), we only spend a few cantos on their story before moving on to the stories of others. While it's unclear exactly why Spenser doesn't spend the same amount of time with this duo than with his other protagonists, it may be related to their interconnected role, which means neither of them carries a heroic story-line themselves, but always relies on the assistance of the other.
While it's a lovely illustration of friendship, it can be a difficult thing to juggle in crafting a good story. Even the love-stories of these two characters cements the closeness of their friendship, since Triamond is married to Cambell's sister, Canacee, and Cambell is married to Triamond's sister, Cambina. While romance is sometimes thought of as a distinct realm of social interaction from friendship, for these two guys, it's all related. Friendship defines every part of their life.
In true friendly fashion, the story of Triamond and Cambell comes from another English author that Spenser greatly admired: Chaucer. Spenser in fact writes a continuation of Chaucer's story, creating a kind of literary "friendship" between him and Chaucer connecting their narratives into one. So cute. We want to get them matching friendship bracelets to show off their bestie status. Too bad they're, uh, really dead.