What letter am I?

My alien has lots of colours. There are yellow, red and gray colours on it's body. It's stronger than all of the things in the whole universe. He can defeat mosters and aliens. He has a big bubbble around him to protecthim. He can defeat 1999999 rhinos at the same time. He has very sharp claws that are electrified as well. He can not be defeated in a battle because he is brave and mighty. He has three gills. He can go under water and go on live land. He has thousands of spikes on its back. That's why I like aliens. S.W