With its wide-open eyes and large tongue, the lion has become a crowd magnet at the castle.
- We have many visitors who travel to Gripsholm just to see it.
They come from all over the world.
It is also not unusual for foreign media to come to report on the lion, says Peter Stenmark, supervisor at Gripsholm Castle.
The theory behind why the lion looks the way it does is that the ambition was never to create a zoologically correct lion, but a heraldic one - similar to those found on coats of arms.
The animal was stuffed sometime in the 18th century.
See how Leo was celebrated and hear why he attracts so many visitors in the clip above.