Zeno of Citrium (c. 334 BC to c.262 BC) Lived in Greece. Teacher and founder of the Stoic school of ancient Greek thought. Stoicism held that a life of Virtue should be lived in accordance with nature. Individual souls are part of the ‘world-soul’ of the divine fire. The universe is cyclical and the goal of life is to live in harmony with nature.
Zeno was probably born on Cyprus and became a relatively wealthy merchant. He moved to Athens and started to study ancient texts, becoming interested in philosophy. In particular he studied under Crates, a leading Cynic philosopher, and is described as leading a spare, ascetic life in line with cynic teachings. Eventually he started to teach himself, gathering a school of pupils who became known as the Stoics from the name of the colonade (the Stoa Poilklie) where he taught.
Stoicism was a development of the cynic teachings. It held that virtue, the highest good, is based on knowledge; the wise live in harmony with the divine Reason (also identified with Fate and Providence) that governs nature, and are indifferent to the vicissitudes of fortune and to pleasure and pain. The identification of the individual ultimately with nature - all people (and other living entities) are manifestations of the one universal spirit and thus all are of equal value - leads to the principle that all should be treated with brotherly love.
The modern usage of "stoic" meaning indifferent to suffering and pain, is an exaggeration of one small element of stoic thought, with the effect of demeaning the whole. From the point of view of the history of green ideas and practice the key quote from Zeno to illustrate the Stoic position is:
“All things are parts of one single system, which is called Nature; the individual life is good when it is in harmony with Nature. ... Virtue consists in a will which is in agreement with Nature”
Zeno's asceticism and rejection of his wealth and the ideas he developed which informed and moderated the development of both the Roman empire and Christianity have echoed down the centuries and directly or indirectly underpinned much subsequent green thought and action. The injunction to "tread lightly on the earth" contains an echo of basic Stoic philosophy.