?480-430 B.C., Greek philosopher and scientist, who held that the world is composed of four elements, air, fire, earth and water, which are governed by the opposing forces of love and discord.

From the souvenir book of the 15th IVU World Vegetarian Congress, India, 1957 (uncorroborated):

. . . continued the Pythagorean tradition. He left no doubt about his opinion of flesh foods : "Will you not put an end to this accursed slaughter? Will you not see that you are destroying yourselves in blind ignorance of soul?"

The Fragments of Empedocles (link to Questia.com) trans. W.E. Leonard Ph.D., Chicago, 1908. Part 2 says much about transmigration of souls and the Orphic/Pythagorean traditions. Extracts:

128
not then with unmixed blood
Of many bulls was ever an altar stained;
But among men twas sacrilege most vile
To reave of life and eat the goodly limbs

130
All things were tame, and gentle toward men,
All beasts and birds, and friendship s flame blew fair..

136
Will ye not cease from this great din of slaughter ?
Will ye not see, unthinking as ye are,
How ye rend one another unbeknown?

137
Hut still is deaf to piteous moan and wail.
Each slits the throat and in his halls prepares
A horrible repast.

139
Ah woe is me! that never a pitiless day
Destroyed me long ago, ere yet my lips
Did meditate this feeding s monstrous crime!

141
Ye wretched, O ye altogether wretched,
Your hands from beans withhold!

translator's notes:

115: With slaughter: i. e., bloodshed of animals, no less than of fellowmen ; it probably refers also to the eating of flesh. Cf. fr. 136.

Fr. 117. Possibly as a punishment for having tasted flesh: "So long as man [in the Orphic belief] has not severed completely his brotherhood with plants and animals, not realized the distinctive marks and attributes of his humanity, he will say with Empedocles: Once on a time a youth was I, and I was a maiden, A bush, a bird, and a fish with scales that gleam in the ocean." Harrison, Proleg. to Study of Greek Religion, p. 590.

Fr. 136. Din of slaughter: killing of animals. Cf. fr. 137 and 115. The reader need hardly be reminded of the Orphic interdict against eating animal food.

Fr. 141. A familiar Pythagorean commandment, on the meaning of which scholars have offered a variety of suggestions. Bodrero (p .149) and others connect it with the doctrine of metem psychosis (cf. fr. 139, 127) ; Burnet (p. 104) well compares it (and kindred Pythagorean rules) to the bizarre taboos of savages. Possibly there was some fancied association, based on shape, with the egg (as E. likened olives to eggs in fr. 79), which, as may be gathered from Plutarch, was held by Orphics and Pythagoreans to be taboo, perhaps as being the principle of life Ccf. Harrison. Prole?., to Study of Greek Religion, p 628).

Engraving of Empedocles

EMPEDOKLÊS - from The Ethics of Diet, Howard Williams, 1st published 1883, text from the 2nd edition, 1896.

The Lives and Opinions of Eminent Philosophers (PDF 15mb)  by Diogenes Laertius (?412-?323 BC), trans. C. D. Yonge B.A., London, 1853. Includes sections on Pythagoras, Empedocles, etc.