Short answers, pulled from the story.
A eukaryote is an organism whose cells have a membrane-bound nucleus, forming the domain Eukaryota or Eukarya. Animals, plants, fungi, seaweeds, and many single-celled organisms are all eukaryotes, standing alongside the two prokaryote groups, the Bacteria and the Archaea.
The word eukaryote comes from the Greek "eu", meaning "true" or "good", and "karyon", meaning "nut" or "kernel". The kernel refers to the nucleus of the cell, the defining feature of the group.
Eukaryotes emerged within the archaeal phylum Promethearchaeota through symbiogenesis. An anaerobic archaeon took in an aerobic proteobacterium that became the mitochondria, and a later union with a cyanobacterium created plants with chloroplasts.
Eukaryotes hold a collective global biomass of 468 gigatons compared to 77 gigatons for prokaryotes, because many eukaryotes are large even though they are fewer in number. Plants alone account for over 81 percent of the total biomass on Earth.
Fossils from the Ruyang Group of China, dating to approximately 1.8 to 1.6 billion years ago, may be the oldest known eukaryotes. Qingshania magnifica from North China, which lived 1.635 billion years ago, is one possible earliest multicellular eukaryote.
Eukaryotes were long divided into the kingdoms Protista, Plantae, Fungi, and Animalia, with Protista named by Ernst Haeckel in 1866. In 1990, Carl Woese, Otto Kandler, and Mark Wheelis proposed domains over kingdoms, uniting the eukaryote kingdoms in the domain Eucarya.