The character pictured above is Sergeant Benton of U.N.I.T. (played by John Levene), who aided the Second, Third, and Fourth Doctor in the original series, but was not generally a "companion" in that he was a regular member of U.N.I.T. and stayed on Earth (with the one exception of "The Three Doctors"). Some of the books on the series consider him a companion for the fact that he did actually travel in the TARDIS that one time, but Danny might actually have a similar supporting role. After all, with Clara spending her time between many of her adventures back on Earth, he may fulfill more of a "grounding" role for her, particularly if he's very active with something interesting going on Earth-side. He could also act as a "call to action" for the Doctor, should he find something interesting that's worth investigating, like the appearance of another Loch Ness Monster (after all, with the new Human/Zygon accord forged in "Day of the Doctor," and the Zygons using such beasts, one of their pets could have gone rogue.) The fact remains, though, that there are so many options when writing that while speculation in itself is immensely enjoyable, in all likelihood, the writers can come up with something completely unexpected and take the series in a new direction that surprises and delights all of us, and in the worst-case scenario that they cannot figure out what to do with Danny Pink, they can find a nice, simple way to get him off the series. After all, they did it with Adric. What do you think? Comment below!
Michael Marcus is a game designer, author, and mad scientist living in Hamtramck, Michigan; his current project list include a series of comic short-stories collectively called "One-Punch," a book on hypnosis and language called "The Prometheus Codex," a collaborative game project called "Art War," and a fun spy story called "The Adventures of Jack Uzi" at http://tinyurl.com/JackUziChannel (for those interested).