Summary: There have been a number of groups and individuals that throughout history have decided to forgo eating meat, usually for animal rights reasons.
Vegetarianism History
In recent history, vegetarianism has become popular again in recent years, after waning a bit after popularity in the 1960s, primarily for animal rights issues. The first time vegetarianism was very popular in the Western world was during the Enlightenment. One of the most high profile groups at this time were the Pythagoreans. Until 1800, vegetarians were actually referred to as Pythagoreans. Going further back, vegetarianism has a longer history in the West, thanked in part to Hinduism and Buddhism, which promote avoiding doing harm to any living thing, as well as due to the belief in reincarnation. Reincarnation is the belief that after death, all living things are reborn in another form, which discourages eating other living things.