Answer by taking a quote from the following article:

Rajinikanth was born on 12 December 1950, in a Maratha family in Bangalore, Mysore State (present day Karnataka). His mother was a housewife, and his father Ramoji Rao Gaekwad, a police constable, He was named Shivaji Rao Gaekwad after Chhatrapati Shivaji, a Maratha warrior King, and was brought up speaking Marathi at home and Kannada outside. Rajinikanth's ancestors hailed from Mavadi Kadepathar, Maharashtra and Nachikuppam, Tamil Nadu. He is the youngest of four siblings in a family consisting of two elder brothers (Satyanarayana Rao and Nageshwara Rao) and a sister (Aswath Balubhai).

Rajinikanth has often been referred to as the most popular film actor in South India by the media and audiences. In 2015, a film about his fandom, For the Love of a Man, premiered at the 71st Venice International Film Festival.  His popularity has been attributed to "his uniquely styled dialogues and idiosyncrasies in films, as well as his political statements and philanthropy". Many also cite reasons for Rajinikanth's popularity as coming from his larger-than-life super-hero appearance in many films, supported by gravity-defying stunts and charismatic expressions, all while attempting to maintain modesty in real-life. Almost every film of Rajinikanth has punchlines delivered by him in an inimitable style, and these punchlines often have a message or even warn the film's antagonists. These dialogues are usually fabricated to create new ones or even be taken in a comical way, but do not fail to create a sense of entertainment among viewers. It is suggested by the media that actresses such as Gouthami and Nayanthara got their initial breakthrough after co-starring with Rajinikanth very early in their careers, giving other aspiring actors the urge to work with him.  Rajinikanth is also the only Indian actor to be featured in the Central Board of Secondary Education (CBSE) syllabus, in a lesson titled From Bus Conductor to Superstar. After opening his first official Twitter account in 2014, Rajinikanth received over 210,000 followers within 24 hours, which according to The Economic Times was deemed by social media research firms as the fastest rate of followers for any Indian celebrity, as well as among the top-10 in the world.  Much like Chuck Norris facts, "Rajinikanth facts" or "Rajinikanth jokes" are widely circulated in text messages and memes over the Internet. These satirical jokes have also inspired several mobile applications for iOS and Android.

What is the most popular movie he has starred in?
In 2015, a film about his fandom, For the Love of a Man, premiered at the 71st Venice International Film Festival.