|Left: a Greek "unmovable" portico (or entrance porch) to a temple, the root of the term "stoicism". Right: a Google-generated definition of stoicism.|
The Stoics derive their name from the Stoa Poikile (Ѻ), the painted colonnade on the north side of the Athenain agora, which was the site of the school. 
It was the cite at which the location from which Zeno of Citium (c.275BC), a follower of Heraclitus, taught Stoicism. Hence, Stoicism derives its name from the Greek "Stoa" or covered walkway or portico, commonly for public use, open at the entrance with columns, usually of the Doric order, lining the side of the building; they created a safe, enveloping, protective atmosphere.
The “stoics”, as they came to be called, supposedly, found the fragments of the work of Heraclitus so obscure that they nicknamed him the "riddler". 
The early Stoa was dominated by its first three heads: the first was the Cypriot Zeno of Citium, who laid the foundations of the system.
On the death (cessation) of Zeno (c.262BC), his successor Cleanthes (c.262BC) (Ѻ) lent a more rigorous dimension to the doctrines of the school, in the face of the increasingly skeptical stance of the Academics (Plato’s academy). He originated new ideas in Stoic physics (Ѻ), and developed Stoicism in accordance with the principles of materialism and pantheism.
The third Stoic school president was Chrysippus, who is credited with the systematic development of the doctrines of the school.
The next major school head was Panaetius (185-109BC) (Ѻ), head of the school from 129 to 109BC, a strong admirer of Plato and Aristotle, who build bridges with the Peripatetics.
His pupil was Posidonius (c.135-51BC) (Ѻ), a scientist, historian, and philosopher, and was the chief philosopher through which Cicero learned Stoicism.
In 45BC, Cicero published On the Nature of the Gods (De Natura Deorum), a discourse on Greek and Roman theologies, namely a dialogue on a comparison of the pros and cons of stoicism, Epicurean theology, and Platonic Academy based skepticism.
Other noted adherents of stoicism or aspects of its logic include: Marcus Aurelius and Thomas Jefferson.
The following are noted quotes:
“The Stoics had a strikingly pure and correct doctrine of the freedom of the will. Moral accountability is involved in the fact that conduct flows from the will, and so from the innermost and most essential nature of man; but the manner in which each man's will shapes itself is only a result of the mighty necessity and divine predestination which govern all the machinery of the universe down to the smallest detail. For his thought also man is responsible, because even our judgments are shaped by the influence of our moral character.”— Friedrich Lange (1875), The History of Materialism, Volume One (pg. 97)
“As you say of yourself, I too am an Epicurian. I consider the genuine (not the imputed) doctrines of Epicurus as containing everything rational in moral philosophy which Greece and Rome have left us. Epictetus indeed, has given us what was good of the stoics; all beyond, of their dogmas, being hypocrisy and grimace. Their great crime was in their calumnies of Epicurus and misrepresentations of his doctrines; in which we lament to see the candid character of Cicero engaging as an accomplice. Diffuse, vapid, rhetorical, but enchanting. His prototype Plato, eloquent as himself, dealing out mysticisms incomprehensible to the human mind, has been deified by certain sects usurping the name of Christians; because, in his foggy conceptions, they found a basis of impenetrable darkness whereon to rear fabrications as delirious, of their own invention. These they fathered blasphemously on him whom they claimed as their founder, but who would disclaim them with the indignation which their caricatures of his religion so justly excite. Of Socrates we have nothing genuine but in the Memorabilia of Xenophon; for Plato makes him one of his Collocutors merely to cover his own whimsies under the mantle of his name; a liberty of which we are told Socrates himself complained. Seneca is indeed a fine moralist, disfiguring his work at times with some Stoicisms, and affecting too much of antithesis and point, yet giving us on the whole a great deal of sound and practical morality.”— Thomas Jefferson (1819), “Letter to William Short”, Oct 31 
1. Stokes, Philip. (2002). Philosophy 100: Essential Thinkers (pg. 15). Enchanted Lion Books.
2. Jefferson, Thomas. (1819). “Letter to William Short” (Ѻ), Oct 31.
3. Sambursky, Samuel. (1959). The Physics of the Stoics. Princeton University Press, 2014.
4. Cicero. (45BC). The Nature of the Gods (Introduction, translation, and notes: Patrick Walsh) (Stoa Poikile, pg. xxxiii). Oxford University Press, 1998.
● Stoicism – Wikipedia.