In Doctor Who (either the old seasons or the revived series), were there ever any people who were Companions of two non-consecutive Doctors? So not people like Rose (9th and 10th) and Clara (11th and 12th), but something more like if Donna (10th) reappeared in the show now (12th).
Depending on your definition of a "Companion", you may wish to add K9 to your list.
He traveled extensively with the 4th Doctor, then made a series of cameo appearances (alongside Sarah Jane Smith) in the 10th Doctor serials.
If you count the audios, Charley Pollard traveled with the Eighth Doctor, then traveled with the Sixth Doctor.