Short answers, pulled from the story.
Gaius flourished between the years 130 and 180 during the reigns of four Roman emperors. Scholars assume he lived from AD 130 to at least AD 179 based on legislation he wrote about within that timeframe.
The Institutes served as an introductory textbook divided into four distinct books covering persons, things, intestate succession, and actions. The first book treated persons and status differences while the second covered rights over things including laws relating to wills.
A palimpsest containing the Institutes of Gaius was discovered by B. G. Niebuhr in 1816. He found it in the chapter library of Verona where some works of St. Jerome had been written over earlier texts.
Later generations found this work more interesting than Justinian's own Institutes because it preserved ancient procedural details no longer visible in later compilations. Much historical information given by Gaius does not appear in Justinian's compilations at all.
The emperor Theodosius II named him alongside Papinian, Ulpian, Modestinus, and Paulus in the Law of Citations. This decree established these five jurists as the primary authorities for deciding cases.