Sigmund is an ancient Giant. In the animated series, he is seen in "Chapter 2: The Midnight Giant" in a flashback and on an image in Wood Man's copy of the book The Giants of Old. In the graphic novel, he is depicted among other giants on the final two pages of "Hilda and the Midnight Giant".
Sigmund is a brown giant with purple glowing eyes. He has a mustache growing on either side of his nose that is the same colour of his body, brown. His body is covered in thick fur.
According to the graphic novels, Sigmund is a cousin of Jorgen, and a rival to Aldinn's leadership. He was known for his long, luxurious fur which he washed twice a day in the sea.
Like the other Ancient Giants, he was eventually driven off the Earth by early humans. Sigmund is kind and was one of the first ones to take the leap into space.