It's comforting to have neighbors like Sheik Khalifa bin Zayed al-Nahyan, the President of the United Arab Emirates and ruler of Abu Dhabi. He had a spare $10 billion to bail Dubai out of its real estate crash in December probably averting a global financial wobble. The grateful emirate next door changed the name of the new 160-story Burj Dubai to Burj Khalifa in his honor. But Sheik Khalifa, 62, who otherwise has a low profile by the standards of Arab princes, is unlikely to let such vanities go to his head. The prince has been a sober steward of Abu Dhabi's oil wealth and is planning for a post-oil future: the emirate aims to be a world leader in sustainable energy.