"Thought." During Thor's visit to Jötunheimr with Loki and Þjálfi, the companions are subjected to a series of tests. The ruler of the giants, Útgarða-Loki, asks Þjálfi what he can do, and the latter says that he would race with whomsoever Útgarða-Loki would bring up. The giant called to him a certain lad, who was named Hugi, and bade him to race against Þjálfi:
Then they held the first heat; and Hugi was so ahead that he turned back to meet Thjálfi at the end of the course. Then said Útgarda-Loki: 'Thou wilt need to lay thyself forward more, Thjálfi, if thou art to win the game; but it is none the less true that never have any men come hither who seemed to me fleeter of foot than this.' Then they began another heat; and when Hugi had reached the course's end, and was turning back, there was still a long bolt-shot to Thjálfi. Then spake Útgarda-Loki: 'Thjálfi appears to me to run this course well, but I do not believe of him now that he will win the game. But it will be made manifest presently, when they run the third heat.' Then they began the heat; but when Hugi had come to the end of the course and turned back, Thjálfi had not yet reached mid-course. Then all said that that game had been proven.
It is later revealed that Hugi was, in fact, the embodiment of Útgarða-Loki's thought, which outpaces all.
- Gylfaginning, 46.