I've read a great deal about Shackleton, and if ever there was a man who epitomised "grace under pressure," it was him. Unflaggingly respected by his men, he was a superb leader, if only in the way that he kept up morale and hope, truly making everyone believe that they would make it. Known to his close friends as "Shackles," it was his force of personality that save him and his men time and again.
He never gave up. Not when his first two attempts to reach the South Pole failed. Not when his ship was crushed by the sheet ice. Not when he and his men spent months floating on an ice floe, or when they sailed to Elephant Island. Or when he and three other men had to cross the South Atlantic in an open boat, through 40 foot waves, to crash land on South Georgia Island, only to cross 40 miles overland through an uncharted mountain range. Bascially, he was a badass, and the best kind -- a good, decent guy who always looked out for his people.
Great Books on Shackleton and the British Trans-Antarctic Expedition:
"Endurance" by Alfred Lansing. I swear it's one of the best pieces of non-fiction you'll ever read.
"South" by Sir Ernest Shackleton. Shackles' own account -- really gripping.
"Shackleton's Boat Journey" by Frank Worsley. The best sailing book I've ever read. The adventure inside the adventure. If you like reading about the sea, this is for you.