Okko, sometimes referred to as The Great Okko, was the chief of a tribe of Ysanna on Ossus. He participated in the Battle of Ossus. He was the father of Jem and Rayf Ysanna. Okko's grandfather rediscovered the Great Jedi Library of Ossus, but kept it a family secret out of fear of looters.
After the battle, Okko and two other Ysanna were trapped in carbonite by the forces of Emperor Palpatine, who was seeking to use the tribe as a means to halt the genetic decay of his last clone. Luke Skywalker soon discovered he was taken to Vjun to the clone laboratory at Bast Castle, but unfortunately, the carbon slabs did not have the controls so he hoped to confront the Emperor and free him. But luck was not with Okko as Palpatine was killed before he could tell the secret to opening the slabs.