What can with certainty be said is that the entry in Wikipedia for the Illuminati is both at once full of otiose speculation and specious completeness and nevertheless lacking in reference to important sources. I chiefly have in mind the essay on Secret Societies and the French Revolution by Una Pope-Hennessy (nee Birch) who traces with admirable clarity the sources of The Perfectabilists who later became known as The Illuminati. This surprises me but on reflection to mention only to deprecate The Illuminati as a leaven of subsequent uprising is an indication of their well known strategy.
Birch accounts Martinez de Pasqually an important forerunner:
Not only was France the home of many masonic lodges, but its social system was riddled with mystical societies which gathered their initiates from among the adepts of masonic grades, and owned allegiance to no supreme council. Swedenborg and Martinez de Pasqually always regarded masonry as a school of instruction, and considered it the elementary and inferior step that led to the higher mysteries. In consequence of their teaching it came about that a great number of sects and rites were instituted in all parts of Europe, whose unity consisted in a common masonic initiation, but whose aims, doctrines, and practices were often irreconcilable. The Martinizists, or followers of Martinez de Pasqually, were a distinctively French sect; they had lodges in Paris in 1754, and also at Toulouse, Poitiers, Marseilles, and other places. The term "Illuminates" is applied to them equally with the Swedenborgians, Martinists, and several germane societies.
Pasqually is said to have been a Rosicrucian adept. His teaching was theurgic and moral, and his avowed object was to develop the somnolent divine faculties in humanity, and to lead man to enter into communication with the invisible, by means of " La Chose," the enigmatic name he gave to the highest secret. He is chiefly interesting as having been the first to permeate the higher grades of French masonry with illuminism, an example followed afterwards with conspicuous success by the disciples of Weishaupt.
Pasqually was followed by Louis Claude de Saint-Martin who further adapted the teaching of his master and became:
He became the mystical philosopher of the Revolution, and the book he published in 1775, " Des Erreurs et de la Verite," produced an immense sensation, comparable to that created by the publication of " La Profession de Foi d'un Vicaire Savoyard." Like Rousseau, he believed in the infinite possibilities of man, holding that Providence had planted a religion in man's heart "which could not be contaminated by priestly traffic, nor tainted by imposture." Rousseau gave the name of conscience to "the innate principle of justice and virtue which, independently of experience and in spite of ourselves, forms the basis of our judgments"; Saint-Martin thought it the divine instinct. On the belief in man's essential goodness both founded their demand for social revolution, claiming an opportunity for men to be indeed men and not slaves, a chance for climbing back to that old God-designed level of happiness from which they had descended. Saint-Martin saw in such a movement the awakening of men from the sleep of death, and with deep conviction he responded to the cry “All men are priests," uttered three centuries earlier by Luther, with the cry "All men are kings " The answer to the social enigmas of the century was whispered by him in the " ternaire sacre " of Liberty, Equality, Fraternity; and it echoed with reverberating clangor through all the lodges of France. Martinist societies were everywhere founded to study the doctrines contained in his book and to expound the teachings of the mystical philosopher who, like Lamartine in a later day, contemplated the Revolution as Christianity applied to politics.
Well, one might say, these societies were no more than the foolery of secret handshakes along with the serious business of fixing the little difficulties of their friends in the commercial and legal spheres. That was true and continues to be the case but prior to the Revolution they were the source of the dissemination of forbidden ideas which culminated in the 'ternaire sacre’ latterly the divine 'laicite’.
Birch offers evidence of the systematic infiltration of French Lodges by the Illuminati under the direction of Weishaupt. Her elegant and extensive essay is well worth reading. Find it on archive.org along with her introduction to The Disciples at Sais by Novalis. The epub format is faulty but the pdf is quite readable on my cheap rubbish tablet.