Life comes in all shapes and sizes, from us humans to bacteria and the tree of life is without doubt one of the great achievements in biology. With that being said, understand that LUCA is not the name of a famous scientist in the field. It is shorthand for Last Universal Common Ancestor, a single cell that lived perhaps 3 or 4 billion years ago, and from which all life has since evolved. Amazingly, every living thing we see around us (and many more that we can only see with the aid of a microscope) is related. I find that comforting!
-An Excerpt from Anthony M. Poole on Evolution
Figure: A phylogenetic tree of life. The very center represents LUCA.