Tammuz 12 is the birthday the sixth Lubavitcher Rebbe, Rabbi Yosef Yitzchak Schneersohn of Lubavitch (1880-1950). This is also the day on which he was liberated from exile to the Soviet gulag 47 years later (see below).
Links:
A short biography
More on Rabbi Yosef Yitzchak of Lubavitch
On the 12th of Tammuz of 1927, the sixth Lubavitcher rebbe, Rabbi Yosef Yitzchak Schneersohn, was officially granted release from his sentence of exile to Kastroma in the interior of Russia.
Twenty-seven days earlier, the Rebbe had been arrested by agents of the GPU and the Yevsektzia ("Jewish Section" of the Communist Party) for his activities to preserve Judaism throughout the Soviet empire and sentenced to death, G-d forbid. International pressure forced the Soviets to commute the sentence to exile and, subsequently, to release him completely. The actual release took place on Tammuz 13, and Tammuz 12-13 is celebrated as a "festival of liberation" by the Chabad-Lubavitch community.
Tammuz 12 is also Rabbi Yosef Yitzchak's birthday (see above)
R. Jacob ben Asher, son of R. Asher ben Yechiel (the Rosh), was one of the most prominent Torah scholars in medieval Europe. His classic work on Jewish law, Arba’ah Turim (known also as Tur), covers every area of Jewish life (in the post-Temple era), presenting the various opinions of previous authorities along with the author’s own decisions. A host of commentaries were written on this work, including one by R. Yosef Caro and another by R. Moshe Isserlis. These two commentaries formed the basis for the Shulchan Aruch (Code of Jewish Law), the definitive guide to Jewish observance until today.
R. Jacob also authored a popular commentary on the Torah, uncovering layers of hidden meaning in the text by way of gematria (and other close analysis of the texts).
Link: Rabbi Jacob ben Asher
This Torah we were given is not of the world, neither is it something extraneous to it. Rather, it is the hidden essence, the primal thought from which all the cosmos and each thing within it extends. It is not about the world, it is the world—the world as its Creator sees it and knows it to be.
The sages of the Talmud told us that the Torah is the blueprint G‑d used to design His creation. There is not a thing that cannot be found there.
Even more, they told us, the Torah is far beyond the world, beyond time, beyond any sort of being. G‑d and His Torah are one, for His thoughts are not extraneous to Him, nor do they effect any change in Him, as do our thoughts. Rather, His thoughts, His wisdom, His desire—all are a simple oneness that does not change.
But He took that infinite wisdom and condensed it a thousandfold, a billionfold, and more, into finite, earthly terms that we could grasp—yet without losing a drop of its purity, of its intimate bond with Him. Then He put it into our hands to learn, to explore and to extend.
So now, when our mind grasps a thought of Torah, thoroughly, with utter clarity, we grasp that inner wisdom. And when we are completely absorbed in the process of thought, comprehension and application, our self and being is grasped by that infinite wisdom which is the essence of all things.
We have grasped it, and it grasps us. In truth, we become that essence.