During his election campaigning in 2014 general elections, the Prime Minister Narendra Modi made a formal visit to Tamil Superstar Rajinikanth's house and sought the latter's support to the BJP. However, Rajini didn't give his nod to Modi then. However, Rajinikanth was gossiped to have assured Modi that he would make political entry by joining BJP in future coarse of action.
Ever since Purachchithalaivi was arrested on the charges of consisting disproportionate assets, speculations have been rife that Rajinikanth would join BJP for sure and to be declared as the CM candidate for 2016 general elections of TN. That's why Modi sent birthday greetings to Rajini through his twitter page both in Tamil and in English.