An unprecedented genius needs a bystander to whom he can show off, a sidekick willing to fulfill the boring obligations of life and an ordinary bloke he can jeer at for being so, well... extraordinarily ordinary. John accomplishes all of these and more with a glowering face, buying groceries and cursing at an uncooperative ATM, carrying a laptop to a crime scene because Sherlock is too disinterested and cozy in his bed sheets or enduring Sherlock's indiscrete denigrations of John's intelligence. These two Londoners make a smashing team, though. Analogous to Clara and the Twelfth Doctor's relationship, John is Sherlock's "carer", the one with more human concerns who is able to discern the priorities of a situation and act promptly. Likewise, the Doctor relies on Clara to mumble apologies to those beaten down by the Scotsman's wrath. She almost acts as a translator, communicating the Doctor's indifferent remarks and clipped responses into a more intelligible language that isn't so unbelievably rude. When the Doctor is miffed (yes, it happens sometimes), Clara acts in his stead. She knows how the traumatic psychological effects of not knowing something can severely hinder the Doctor's performance. And there are no second chances permitted when the universe is at stake. Independent, feisty and unpredictable, these companions are their employers' second shadows. Sometimes, however, it's quite difficult to know who's the boss.