Can Superman be defeated without kryptonite?

By Johel Khan
works at Stencil Bangladesh LTD

Yes, unfortunately he can be killed without the use of magic or Kryptonite. Superman was first killed by the Kryptonian abomination named Doomsday during The Death of Superman arc. Not only did that monster put the Man of Steel out of action before meeting his own demise, he also took out the roster of Justice League of America. However, Doomsday is not the only thing that can kill Superman.
There are other factors that might be proven fatal for him too. Such as Red Sun Radiation and Ionized Radiation (such as Nukes used in The Dark Knight Returns). These factors will not immediately kill him but will render him to a state where he will be nothing more than a mere mortal. Any fatal attempt on his life could do it with ease.

I hope this helps. Cheers!