The partner of Tony Stark's father, who ran the company while Tony did not, and who hired the men who were supposed to kill him.
Obadiah Stane is the mentor who was already the enemy. He took over Stark Industries after Howard died, kept it running through Tony’s absence, and hired the Ten Rings to kill him when Tony finally started paying attention to what the company was selling.
Jeff Bridges plays him warm, which is the whole trick. He is the only person in the film who is kind to Tony without visibly wanting anything, right up to the moment he takes the arc reactor out of his chest and explains why.