Rabbi Shimon was a fifth-generation Tanna, according to the classification of Rabbi Adin Steinsaltz in The Talmud A Reference Guide, who flourished in years 135 C.E. - 170 C.E. He was a student of Rabbi Akiva, and a contemporary of Rabbi Shimon ben Gamliel II, who was the Nasi, the Scholar-President, and of Rabbi Meir and Rabbi Yehudah ben Ilai, among other great contemporaries. He was a complex individual, a Torah giant who was influenced by his father, Yochai, by his great teacher, Rabbi Akiva, and by the events of his day. His main achievement was the authorship of the Zohar, the Torat HaNistar, the hidden Torah that he received orally from his teacher, Rabbi Akiva. The latter is described in the Talmud as the only one of a group of four outstanding Torah scholars who attempted to enter the Pardes, the Orchard, a metaphor for the depths of Kabbalah, Jewish Mysticism, who was able to emerge safely.
His father was a man of considerable honor among the Jewish People. Yochai was a pacifist, was well-liked by the Romans, and was a bitter opponent of the revolt against Rome led by Rabbi Akiva and bar Kochba.
Although Shimon was extremely loyal to Rabbi Akiva, he rejected some of his methods of Torah scholarship, such as the inference of laws from extra words prepositions and connectives, in the text of the Torah. He believed that for the purpose of inferring halachot, rules of Jewish Law, the text should be interpreted plainly. He also rejected the pilpulistic method of his colleague, Rabbi Yehudah ben Ilai. He was a believer in using the Taamei HaMitzvot, the reasons for the commandments, as a guide in understanding them.
How remarkable it is that despite his insistence on learning the simple meaning of the Torah from its plain text, he was the one who saw the Torah as well on an entirely different level, as the Torat HaSod, the Secret Torah.
Another paradox in the thought of Rabbi Shimon bar Yochai is in his attitude towards Rome. In Bereshit 33:4, where Esav kisses Yaakov, there are dots over the word meaning and he kissed him. Rabbi Shimon says, It is a well-known principle of Law that Esav hates Yaakov, but here Esavs mercies were aroused, and he kissed him with all his heart. Yet his sense of fairness did not allow him to adopt a leniency even with regard to a hated enemy, and he said Stealing from an idol-worshipper is called stealing, and is forbidden absolutely.
Once, when Rabbi Shimon was together with Rabbi Yehudah ben Ilai and Rabbi Yose ben Chalafta, Rabbi Yehudah praised the Romans for their construction of markets, bridges and bathhouses. Rabbi Yose remained silent. But Rabbi Shimon bar Yochai said that all those engineering marvels were made for their own self-interest. When the Romans heard this, they rewarded Yehudah by appointing him to a position in government. Rabbi Yose, for not supporting him, was punished by exile. For his disparagement of the Romans, Rabbi Shimon was condemned to death.
To escape this punishment, Rabbi Shimon fled with his son to a cave. There they remained for thirteen years, studying Torah together, both the Revealed and the Hidden Torah. Rabbi Shimon wrote down the latter material for the first time in a book called the Zohar, Splendor, or Radiance.
The first time Rabbi Shimon came out of the cave, he was completely "out of tune" with the people of his generation. He observed Jews farming the land, and engaged in other normal pursuits, and made known his disapproval, "How can people engage themselves in matters of this world and neglect matters of the next world?" Whereupon a Heavenly Voice was heard, which said "Bar Yochai, go back to the cave! You are no longer fit for the company of other human beings." Rabbi Shimon went back to the cave, reoriented his perspective, and emerged again. This time, he was able to interact with the people of his generation, and become a great teacher of Torah, the Revealed and the Hidden.
Lag BaOmer, according to Tradition, was the day of the petirah of Rabbi Shimon bar Yochai and, according to his wishes, the Yahtzeit was to be observed as a holiday. This is done throughout the Jewish world, but the main celebration is at Meiron, the burial place of Rabbi Shimon and his son, Elazar, where thousands of Jews gather to light torches, sing (several stanzas of a favorite song and its chorus appear below) and dance in honor of the G-dly Tanna:
Bar Yochai! You were anointed You are fortunate;
With oil of joy from your fellows.
Bar Yochai! In a goodly dwelling did you settle
On the day you ran, the day you fled;
In rocky caves where you stopped
There you acquired your glory and your strength.
Bar Yochai! Like standing shittim beams,
The teachings of G-d they study;
An extraordinary light is the light of the fire
That they kindle they, your teachers, will teach you.
Bar Yochai! You came to a Field of Apples
And entered it to pick confections;
The mystery of Torah with blossoms and flowers -
Let us create man was said because of you.
Bar Yochai! At a wondrous light in lofty heights,
You feared to stare for it is great,
Such hiddenness that one calls her, Naught;
You declared that no eye could see You.
Bar Yochai! You were anointed you are fortunate;
With oil of joy from your fellows.
Sources: Orthodox Union