Disclaimerage: So not mine. Written for fun, not profit.
He takes after his mother in looks and personality. She was an unremarkable chuunin, content to retire from active duty after her son was born, and his memories of her are full of laughter and patient smiles and the occasional terrifying bellow when he pushed his limits just a little too far.
His father is a more elusive figure - a jounin, fond of traditional dress, tall to the point of imposing, never one to participate in his wife and son's lively conversations - but Iruka remembers being carried on his shoulders or under one arm; he knows with absolute conviction that his father loved children.
Even before his parents die, he is one of the least motivated students in his class. Before the Kyuubi, he has no inclination to be a shinobi beyond some general sense of filial duty. After the Kyuubi, he sees no reason to try.
What finally motivates him - even if he'd never admit it - is the realization that his teachers expect him to fail, and the only way he knows to get back at them (short of rigging tripwires around the blackboard again) is to prove them utterly and completely wrong.
Iruka has always been exactly as stubborn as he chooses to be.
He has outlived a little over a quarter of his students. He would know; he keeps track.
More often than not he strays from the sanctioned curriculum. There is nothing in his training or his classroom manuals that requires him to tell his students to be careful, to keep an eye on each other, to keep their missions in perspective and most of all to not get killed.
Sometimes this approach has caused problems, but he doesn't mind. He has little time and less patience for parents who consider their daughters and sons weapons or instruments or a means to an end. In his classroom he is something close to untouchable; he has argued with clan heads and squad leaders and S-rank shinobi who have either forgotten or never knew what it was like to be an ordinary child.
There are many many reasons he will never be a jounin. Winning these battles is just the most important of them.
He has never and probably will never be able to articulate exactly what one particular student means to him.
All the same, he is as proud of Uzumaki Naruto as any parent could ever hope to be.