Apple CEO Tim Cook is clearly a bright and talented guy, but until the company delivers a product post-Jobs that wows and not just new iterations of the same old things, he’ll be judged with suspicion. And even though he seems to be more progressive than his late boss in terms of charitable giving and environmentalism, he’s apparently just as scary when in business mode. From Haunted Empire: The Job After Steve Jobs, Yukari Iwatani Kane’s new book which has been excerpted in the Wall Street Journal:

“Meetings with Cook could be terrifying. He exuded a Zenlike calm and didn’t waste words. ‘Talk about your numbers. Put your spreadsheet up,’ he’d say as he nursed a Mountain Dew. (Some staffers wondered why he wasn’t bouncing off the walls from the caffeine.) When Cook turned the spotlight on someone, he hammered them with questions until he was satisfied. ‘Why is that?’ ‘What do you mean?’ ‘I don’t understand. Why are you not making it clear?’ He was known to ask the same exact question 10 times in a row.

Cook also knew the power of silence. He could do more with a pause than Jobs ever could with an epithet. When someone was unable to answer a question, Cook would sit without a word while people stared at the table and shifted in their seats. The silence would be so intense and uncomfortable that everyone in the room wanted to back away. Unperturbed, Cook didn’t move a finger as he focused his eyes on his squirming target. Sometimes he would take an energy bar from his pocket while he waited for an answer, and the hush would be broken only by the crackling of the wrapper.

Even in Apple’s unrelenting culture, Cook’s meetings stood out as harsh. On one occasion, a manager from another group who was sitting in was shocked to hear Cook tell an underling, ‘That number is wrong. Get out of here.’

Cook’s quarterly reviews were especially torturous because Cook would grind through the minutiae as he categorized what worked and what didn’t, using yellow Post-its. His managers crossed their fingers in the hopes of emerging unscathed. ‘We’re safe as long as we’re not at the back of the pack,’ they would say to each other.

Cook demonstrated the same level of austerity and discipline in his life as he did in his work. He woke up at 4:30 or 5 a.m. and hit the gym several times a week. He ate protein bars throughout the day and had simple meals like chicken and rice for lunch.

His stamina was inhuman. He could fly to Asia, spend three days there, fly back, land at 7 a.m. at the airport and be in the office by 8:30, interrogating someone about some numbers.

Cook was also relentlessly frugal. For many years, he lived in a rental unit in a dingy ranch-style building with no air conditioning.”