Non-removable stain after cooking

What is this stainless steel stain?

I just bought a stainless steel 3-ply pan and cooked some fried eggs to test it. I ended up with this impossible to clean golden stain that felt sticky to the touch.

What is it? How did this happen? How can I clean it?

What is this stainless steel stain?

I just bought a stainless steel 3-ply pan and cooked some fried eggs to test it. I ended up with this impossible to clean golden stain that felt sticky to the touch.

What is it? How did this happen? How can I clean it?