The Host (and The Author) is a character created by the Cyndago team and played by the golden-voiced YouTuber himself, Markiplier.
Originally introduced as The Author in the YouTube videos "Danger In Fiction" and "Danger In Fiction II," he was intended to be debuted as The Host in a third video. Unfortunately, this third video didn't turn out to the group's satisfaction and was scrapped, save for a short intro used to clickbait an April Fool's joke, "Danger In Fiction: The Host," in 2014. According to Cyndago's Facebook page, there were intentions to continue the character's story for real in the future, but this never panned out, and Cyndago was officially ended in October of 2015.
However this was not the end for the Host, who would make one final (to date) appearance in a Markiplier skit entitled "Markiplier TV." In the video, he is seen seated at a meeting among Markiplier's many "egos," narrating the happenings of the day slightly ahead of them happening, thus revealing the Host as having precognitive abilities (something which many fans have theorized would allow him to navigate the world with relative ease despite being blind).
Despite, or perhaps because of, how little is known about the intended canon facts about the character, The Host has proven extremely popular among fans, spawning hundreds if not thousands of pieces of fanart, fanfiction, and even cosplay.
"I've been given a gift--
whatever I write, happens!"
"You see, cooperation is key.
Working together, and believing in
one another--that's essential."