Shihab al-Din Yahya al-Suhrawardi (1154-91), commonly known as Suhrawardi, was a Persian philosopher, a Sufi and founder of the Illuminationist philosophy or "Oriental Theosophy."
This intellectual whose life spanned a period of less than forty years in the middle of the twelfth century, produced a series of highly assured works which established him as the founder of a new school of philosophy in the Muslim world, the school of Illuminationist philosophy (hikmat al-ishraq).
He is given the honorific title Shaikh al-Ishraq or "Master of Illumination."
Although arising out of the peripatetic philosophy developed by Ibn Sina, Suhrawardi's Illuminationist philosophy is critical of several of the positions taken by Ibn Sina, and radically departs from the latter through the creation of a symbolic language to give expression to his metaphysics and cosmology, his 'science of lights'.
The fundamental constituent of reality for Suhrawardi is pure, immaterial light, than which nothing is more manifest, and which unfolds from the Light of Lights in emanationist fashion through a descending order of lights of ever diminishing intensity; through complex interactions, these in turn give rise to horizontal arrays of lights, similar in concept to the Platonic Forms, which govern the species of mundane reality.
Suhrawardi also elaborated the idea of an independent, intermediary world, the imaginal world (alam al-mithal). His views have exerted a powerful influence down to this day, particularly through Mulla Sadra's adaptation of his concept of intensity and gradation to existence, wherein he combined Peripatetic and Illuminationist descriptions of reality.
He clearly intended his philosophy to make a distinctive break with the previous peripatetic tradition of Ibn Sina, but the significance of this break has been interpreted in a number of ways.
For subsequent Islamic philosophy, he was above all the conceiver and main proponent of the theory of the primacy of quiddity. While the predominant trend in Western scholarship has been to depict him as the originator of a distinctive mystical and esoteric philosophy, recent Western scholarship has emphasized his critique of peripatetic logic and epistemology and his own theories in these fields.
The integrity of Suhrawardi's complex philosophy is achieved in no small measure by the elegance and refinement of his means of expression.
In the philosophical tradition which continued after the Mongol period in Iran and further east in India, Suhrawardi stands second only to Ibn Sina. Perhaps the greatest testimony to his lasting importance is the fact that to this day in Iran philosophers are still informally classified as either mashsha'i (peripatetic) or ishraqi, depending on their leaning towards rationality or mysticism.

                                                                               (Source: muslimphilosophy.com)