Although Aleinu was composed by Yehoshua bin Nun, and the Anshei K’neses HaG’dolah instituted its inclusion in the Malchiyus section of tefilas Musaf on Rosh HaShanah, it was Rabban Yochanan ben Zakai who instituted saying it daily after each tefilah. He did this to strengthen the emunah and spirits of klal Yisrael, who were living through the painful times of the destruction of the second Beis HaMikdash.
We recite Aleinu daily, many of us three times a day; perhaps because we have grown so accustomed to saying it, many of us unfortunately do not appreciate the significance and importance of this tefilah. In fact, we are often mentally on our way to the next part of our day as we fly through this awesome tefilah.