‘Sai’ is another synonym of God. Literally it means omnipotent or omnipresent. Sai Baba refers to a 19th century Muslim faqir i.e. hermit who renounced the worldly affairs and left himself at the mercy of God or Sai. He spoke almost nothing except Sai. In other words he tried to point out that everything is God or Sai. The seer gained popularity over his selfless existence but has gained even more popularity in this century. The obvious reason is, the mouth to ear, reasoning that worshiping his deity produce desired results. The popularity of new deity is so much that deiform of Sai Baba now share dais with Ram and Sita in a temple as per picture below:
But religious shops aka temples are helpless for these are also governed by demand and supply rules and demand for Sai out weigh the consideration for archaeological etymology of God in question.
An Hindu Shankracharya (Hindu counterpart of Christian apostle) has openly denounced the practice of worshipping Sai Baba as contrary to Hindu religion. So much so that recently a petition was filed in Supreme Court of India claiming infringement of freedom of religion but it deftly declined.
The development is interesting as Hindu tradition of worshipping image is a practice which is dated back to over ten thousand years if not more. The fact that a Muslim Seer has been deiformed is a new challenge. But as it happens, most of worshippers of Sai are not aware of the complete biography. At least none could tell me when asked. Some of worshippers are close friends and relatives therefore I had to be polite and non invasive but I do not think it affected the result.
Any how the teaching of the Baba, to surrender, is yet to reach the followers who throng the temples seeking more possessions and to protect existing ones.