First appearance: Journey into Mystery #102, March 1964
History: the sister of Heimdall and childhood friend of Thor and Balder the Brave, she had been born with golden hair like many other Asgardians, but due to a nasty trick played by Loki, and an attempt he made to fix it, she developed black hair instead. Thor thought she looked even lovelier as a brunette, and thus, Loki's attempt to ruin their happiness failed.
Current status: on Earth with a few other Asgardians, Thor included, in Oklahoma.
Was subjected to the following act of discrimination: during 2007-2008, when J. Michael Stracynski was writing Thor, and the Asgardians were reborn on Earth in the bodies of humans, he had Sif reborn in the body of an old woman suffering from cancer, with only a special mirror to help show her real image.
What's wrong with how this was done? Knowing Stracynski's modus operandi since the turn of the century, it doesn't take much to figure for starters that anything he does will be like turning gold into straw instead of lovely brunette hair - and his subversion of Sif to the sidelines during that weak story was, for lack of a better word, insulting.
Thankfully, as the storyline ended, her whereabouts were figured out, and she was taken out of the old woman's body and restored to normal. And we can only hope Stracynski never gets his mitts on Thor and the other Asgardians ever again, nor Spider-Man, for that matter.