The film starts off with Ramaswamy Naicker(Satyaraj) as a young man who responds to injustices happening around him in his own way - sometimes mischievously and sometimes seriously. When one of his acts results in his father, a Municipal Councilor, being insulted, Ramaswamy is kicked out of the house. He goes on a pilgrimage to Kasi but is further disillusioned by what goes on under the name of religion and after returning home, takes over the family business and eventually goes on to become the Municipal Chairman of Erode. He is convinced to join the Congress party by Acharya Vinoba Bhave and Rajaji, who believe that his presence will help dispel the party's image of being only for the upper castes. But when he realizes that his priorities are different from the party's, he quits and becomes a social reformer who wants everybody to develop self-respect.

The film succeeds in portraying Periyaar as someone who believed strongly in himself and wasn't ready to give up on his beliefs or ideals for anything or anybody. While individual sequences focus on many of his qualities, what we get out of all them is his stubbornness when it came to something he believed in. Most of the significant events in his life - his quitting the Congress party and Annadurai splitting from him, to name a couple - happened because of this one characteristic and that is what makes the film interesting too. It is easy to admire him when he gets a widow remarried or fights for the rights of the lower castes but it is when he is stubborn in going against popular opinion(like when he proposes new ways of printing Tamil letters to save money) that the movie is most interesting.

The movie has an episodic feel initially and feels jerky. In the attempt to showcase everything that Satyaraj tries to set right, the film jumps from one episode to another rather abruptly and feels like a collection of vignettes from his life without a connecting thread. But as Satyaraj gains focus in life, the movie does too and begins to feel more like a biography should. From around the time he returns from Kasi, there is a logical progression in the turns his life takes and so the movie too begins to flow more smoothly. We understand why he joins the Congress, why he spends most of his time on the road, why he quits the party, etc. and this understanding leads to admiration.

Biographies, by definition, focus on their subject but good biographies also let other characters flower. They play off of the protagonist of the biography but atleast some of them have their individualities and make an impression. That doesn't happen in Periyaar. Everybody other than Satyaraj has little screen time and they barely make an impression. They stay in the picture only as long as they revolve around Satyaraj. Also, Satyaraj is never shown in a bad light while everybody in the non-Periyaar camp is made a caricature. Even his mother isn't spared as her religious nature is portrayed in an over-the-top way and the only Brahmins we see are those who are corrected or helped by Satyaraj and end up changing their initial impressions about him. So the movie seems too one-sided and makes us question how much of Periyaar's life was not shown.

Just when we have resigned ourselves to the fact that we will only see Satyaraj in ridiculous spoofs and movies designed to boost his son Sibi, he shows us in Periyaar what a fine actor he can be. We initially see the actor rather than the character as he plays tricks on his mom or questions social practices with his trademark nakkal. But he grows into the character as it matures and makes us forget who we are watching. By the time he is hidden under the white wig and beard, the transformation is complete and his body language and quivering voice create a very believable old man who is still young at heart. Kushboo is dignified in a short role while Jyothirmayi earns some sympathy as a wife unable to understand her husband but still supportive of him. A host of other actors(Ilavarasu, Y.G.Mahendran, 'Nizhalgal' Ravi, etc.) have small parts. The actors playing Annadurai and Rajaji resemble their real-life counterparts very well.