We first met Nardole when he was River Song's assistant, before he was incorporated into King Hydroflax's body. That was cute, and then he appeared in the 2016 Christmas Special. By that time Nardole had apparently spent quite a lot of time with Capaldi's Doctor, though of course we saw none of that because no episodes were shown to us that year. Now we're in Season 10, and Nardole is still with us. He spent 10+ months living in Cardiff working on the Doctor Whom season. Supposedly he's here because he asked Stephen Moffatt to come to the show, and that's it. Really? That makes no sense. For character-continuity, Nardole had to be reassembled in some way, and in The Pilot we saw a mechanical piece apparently drop off his hand. We're supposed to learn more as the season progresses. And, Nardole isn't being billed as The Companion, but he's appearing in episodes enough that we should consider him as A Companion.
Matt Lucas: “As the series goes on, I think Bill and Nardole find they have more in common and challenge the Doctor more. Nardole grows to appreciate Bill and what she brings to the TARDIS. The Doctor has grown weary of Nardole but as the series goes on, I think he comes to appreciate what he has to offer. As far as Nardole is concerned, the less drama, the better. So when a human comes on board he’s not exactly delighted. He doesn’t look up to humans either. He thinks they’re of little consequence (he’s right). I think Nardole wants to stay focused on the task he’s been given and doesn’t appreciate the distraction for the Doctor that Bill provides. You couldn’t go through a whole series with him being as cartoonish as he was in ‘The Husbands of River Song’. That episode was played for laughs because it was a Christmas Special. We get to learn more about him and why he’s there. He has a purpose.”
Nardole has a "purpose" for being present, there's a "task he's been given". Nardole is not human.
Between the comedy element, he's been shown to have quite a lot of knowledge/skill. For example, the Doctor trusted him to fly the TARDIS and it was okay that Nardole had a side adventure in ancient China before arriving in Manhattan for the thing with Doctor Mysterio.
Nardole had spent time working with River Song. Did River teach him the TARDIS? What is his cultural background with which he could grok the TARDIS? Is this task from his culture? From some other organization?
