Trending on Twitter, tributes the world's last male northern white rhino who was put down earlier this week at 45 years of age at a Kenyan wildlife conservatory.
One tweeter quotes photographer Ami Vitale saying, "Today we are witnessing the extinction of a species that had survived for millions of years but could not survive mankind."
Another tweet reads, "This story is horribly sad, but its beautiful to see him being loved and comforted in his final moments."
Here's a clip of Sudan's last moments from National Geographic who documented his life.