Sidekick-o-rama : Frobisher

Colin Baker's sixth Doctor perhaps wasn't best served by his TV stories.

He was written too moody, even trying to murder his companion in his debut story as well as pushing a foe into an acid bath early in his run.

Character aside, the plots were mired in continuity. Witness Attack of the Cybermen which required knowledge of an 18 year-old TV story that at that time the BBC had lost.

But his strongest stories were in the Marvel comics.

As had been the norm with previous regenerations, the Sixth initially had a comics-only companion.

Writer Steve Parkhouse decided to take full advantage of the unlimited special effects budget and go with a shape-changing alien who chose to stay as a penguin for "personal reasons".

Doctor Who : Voyager. (Parkhouse, Ridgway, Hart)

Frobisher was a Philip Marlow-esque private eye. We first meet him disguised as a telephone, investigating an adulterous husband.
It's quite apt that the Doctor in his supposedly shape-changing Tardis is accompanied by a shape-changer who stays in just as incongruous a form.

Doctor Who : Voyager. (Parkhouse, Ridgway, Hart)

He's a charming addition to the Who myths and a rare example of a TV franchise taking advantage of the artistic freedom of comics.
Also, somewhat improbably, some of his tales were written by future comics great Grant Morrison, including Frobisher's last as a regular companion to the Sixth Doctor.
They're available in reprints and are well worth a read.