Animals Hate Him: In Uskerty, he winds up being attacked by bees and pestered by a goose, which then proceeds to eat his father's signet ring.
Buffy Speak: While he tries to be professional, Martin lacks Douglas's impressive vocabulary, and occasionally lapses into this.
Martin: But the thing is, we’ve taken away all the things that couldn't possibly have happened, so I suppose the only thing that’s left, even though it seems really weird, must be the thing that did happen, in fact.
Expecting Someone Taller: Is constantly on the receiving end of this when people fail to acknowledge him as the Captain.
Geek Physiques: Implied to be small and spindly. Has trouble getting people to recognise him as an authority figure. This can be a bit jarring when it comes to the promotional pictures, since Benedict Cumberbatch is actually six feet tall.
Green-Eyed Monster: Towards Douglas, who looks the part of an airline captain in addition to having the skills. Also towards the actor Martin in "Rotterdam."
Grew a Spine: Series 4 shows him being somewhat more assertive and confident.
Not so Above It All: Despite being a stickler for safety and professionalism, Martin is occasionally seen indulging his sense of humour during his cabin addresses on cargo flights, and goes out of his way to throw an improvised Christmas party for Arthur in the flight deck.
Sickly Neurotic Geek: Has an "abnormality of the inner ear" that makes him reluctant to go swimming without earplugs in "Ipswitch", worries that being able to smell bacon might be a sign of impending doom in "Xinzhou", and plays up his injury to get out of hard work in "Ottery St. Mary".
"Well Done, Son" Guy: Martin's late father tried to steer him away from becoming a pilot after he repeatedly failed his exams. Martin deeply regrets that his father never got to see him fulfill his dream.
Bunny-Ears Lawyer: Carolyn is fully aware of his love of Zany Schemes, disregard for rules, and tendency to steal expensive whiskey, but he remains employed because of his skill as a pilot, as well as his general talent for getting MJN out of virtually any kind of trouble.
Captain Obvious: A case of Tropes Are Not Bad- he does it in the most gloriously snarky way possible, and it's kind of a necessity in order to convey to the audience what's happening given the format.
Cloudcuckoolander: It's camouflaged by his impressive vocabulary, intellect, and snark, but Douglas certainly has a bizarre sense of humour and a rather wacky imagination- his story about St Mary being eaten by otters is a good example, as are most of his cabin addresses and word games.
Tall, Dark and Snarky: Possibly, depending on how canon the cast picture is. Roger Allam has dark hair, so most fans tend to assume that this applies to Douglas as well. Douglas's height, however, and his snark especially, fit this trope to a tee.
Ultimate Job Security: An awful lot of his behaviour — including low-flying GERTI over some polar bears having accidentally left the cabin address on so everyone on board can hear Martin screaming at him to stop and stealing from the CEO at least once a year — should at least get him suspended or disciplined. Justified by the fact that there isn't an alternative given MJN is an Oddly Small Organisation, and he is very good at getting them out of tight spots at very short notice.
Weasel Co-Worker: Zigzagged. Douglas is certainly sneaky and a slacker, and often winds up getting Martin in more trouble than himself, but he is highly competent as a pilot, and is often the one who winds up bailing MJN out when trouble strikes.
The Watson: He's usually the one to ask the pilots questions related to aviation and aeroplanes, which helps clarify the piece-that's-fallen-off-GERTI-of-the-week for the benefit of the audience. He becomes a much more literal Watson to Martin's"Sherlock" in the episode "Paris."