I love tumblr. I’m involved in a discussion over which  Harry Potter house Ianto Jones would belong in. I’m leaning towards Slytherin myself.
I’ve been trying to work this one out myself – I think it’s rare to come across someone who could fall neatly into either Hufflepuff or Slytherin.  He’s clever enough to be a Ravenclaw and brave enough to be a Gryffindor, but these don’t really define his personality, in the way that Martha and Tosh are Ravenclaws through and through, and I would probably need a separate post to count the ways in which Jack and Gwen are practically poster-children Gryffindors.
But my perception of Ianto – albeit one that has been more shaped by fanon than canon – is that of someone who is thoughtful, hard-working, and is gifted with immeasurable amounts of patience to deal with all the juvenile drama that is Torchwood Three.  Never mind that Hufflepuff is the house that gets the least attention, given all the juvenile drama and one-upmanship between the other houses.  He is boneheadedly loyal to the people he loves – while Lisa is the most obvious example of this, let’s not forget that time he was literally boneheaded enough to headbutt a cannibal to save Tosh.  Even at a time when he might not have even liked them much, they were his people. Â
This is where we start seeing the Slytherin qualities: if his overriding, above-all-else motivation is to protect his people, then his resourcefulness, determination, and devious cunning to that end are to make any Slytherin cry with envy.  And if there’s one Hufflepuff quality he doesn’t have in spades, it’s honesty.  The man conned Jack Harkness, for Rassilon’s sake!  If the Hufflepuff in him acquiesces to Jack’s orders, then the Slytherin in him is picking his battles carefully and going behind Jack’s back to fix it his way – look at Adrift.  While he doesn’t come off as ambitious on the surface, there might be something to that in his backstory – that he was never proud of his upbringing and ran away to London, got a job at a top-secret alien James Bond institute and wore suits all the time.  And despite his apparent ease in the role of Jack’s subordinate, he gives very much a ‘power-behind-the-throne’ vibe – he’d probably even manage to keep Torchwood a secret, singlehandedly, if it weren’t for the SUV, and Owen ordering pizza, and Jack constantly showing off.
So yeah, I’m still a bit stumped on this one.  Anybody want to add some insight?
I would place Ianto firmly in Slytherin.  Hufflepuffs are loyal, yes, but they’re also accepting, universally kind, and do their best to play by the rules regardless of their opponent’s behaviour.  Ianto is loyal, but he’s only loyal to those whom he loves.  He isn’t loyal to causes; if he were loyal to Queen and Country, he wouldn’t have rescued Lisa and then secreted her into Torchwood Three right under Captain Harkness’ nose.  He is loyal to people, and implacably so.  Ianto is loyal to Lisa, to Jack, to Tosh and Gwen and (yes, even) Owen, and maybe even to his family, but to no one and nothing else.
Intelligence, patience, thoughtfulness, and a willingness to work hard are not exclusively Hufflepuff qualities, nor are they always the saintly qualities they sound at first.  All of those qualities are necessary to be successful at anything, including ruthless ambition.  What sets Hufflepuffs apart are things Ianto doesn’t have, morals against things Ianto is unflinchingly willing to do.
Unlike a Hufflepuff, Ianto doesn’t hesitate to lie, cheat, steal, or injure to get what he wants.  He lies to Jack multiple times for Lisa and to protect his own pride, he steals in CoE when he has to, he routinely covers up the less-than-legal things Torchwood does, and he’s wicked with a stun gun.  He puts the entire Earth, and possibly the entire Universe, at risk for even a chance at saving the woman he loves (and Ianto is anything but stupid, he would have known the risks).  He’s even willing to, if not outright kidnap, at least take under dubious circumstances his own niece for experimentation in CoE.  He’s manipulative, cunning, clever, implacable, and always gets what he wants.  That, my friends, is a Slytherin through and through.
I would also argue, however, that Jack is a Slytherin.  Oh, he acts like a Gryffindor when he gets the chance.  He’s got the bluster, the arrogance, the recklessness, the showboat of a Gryffindor.  He desperately, desperately wants to be a Gryffindor (and that want is part of why he keeps Gwen around).  What he doesn’t have, however, are the unbending morals of a Gryffindor.  Jack is willing to do unsavory things for greater purposes.  Jack is willing to kill (Steven), to compromise (Jasmine, the first set of children in CoE), to torture (Countrycide, Beth), to lie (practically everyone he’s ever met ever, Alice—though she, bless her, is too smart for him), and to otherwise act in terrible ways for his own or the world’s benefit.  He wants to be the Doctor’s Gryffindor, Gwen’s Gryffindor, Rose’s Gryffindor, but he isn’t, and I doubt very much he ever will be.
