Gadolinium (Gd) is a chemical element with atomic number 64. It is named after Swedish-Finnish chemist Johan Gadolin. He actually didn't discover gadolinium, but he was the first to discover rare earth metals in general, and specifically the element yttrium.
There are six stable and naturally occurring gadolinium isotopes, and 158Gd is the most abundant of them, with 64 protons and 94 neutrons.
While there are no large scale industrial uses for gadolinium, it is sometimes used for the detection and treatment of certain cancers, and also sometimes used as the green color component in TV screens.