Mahesh Das (Hindi pronunciation: [məɦeːɕə d̪ɑːsə]; 1528 – 16 February 1586), popularly known by his title Rajah Birbal (lit. 'The Quick Thinker'), was an Indian minister and commander of the Mughal Empire. He is mostly known in the Indian subcontinent for the folk tales which focus on his wit. He was appointed by Akbar and was one of his most important courtiers, part of a group called the navaratnas (nine jewels). In February 1586, he led an army to crush an unrest in the north-west Indian subcontinent now modern day Swat District Pakistan where he was killed along with many troops in an ambush which turned into a full-scale battle against rebelling Yusufzai and adjoining tribes. He was the only Hindu to adopt Din-i Ilahi, the religion founded by Akbar.

Local folk tales emerged primarily in 19th century involving his interactions with Akbar, thus became even more of a semi-fictional legendary figure across the Indian subcontinent. However, these stories have generally been described as fictional by modern historians.

Birbal was born as Mahesh Das in 1528. According to historical and literary evidence presented in Raja Birbal: Life and Times, Birbal was born into a Brahmbhatt family of Ganga Das in the village of Tribikrampur (now Tikwapur), in present-day Kanpur District of Uttar Pradesh.

He was educated in Hindi, Sanskrit and Persian, and Bengali. He wrote prose, specialised in music and poetry in the Braj language, thus gaining fame. He served at the Rajput court of Jaipur and Raja Ram Chandra of Rewa, under the name 'Brahma Kavi' before he joined the Mughal court in 1569. Birbal's economic and social status improved after marrying a woman of a wealthy family, contrary to the notion that he was on poor economic terms before his appointment at Mughal Emperor Akbar's imperial court.

The details and year of his first meeting with Akbar and his employment at the court are disputed but estimated to be between 1556 and 1562. He became the "Kavi Priya" (poet laureate) of the Emperor within a few years of his appointment. Akbar bestowed upon him the name 'Birbal' with the title "Raja", by which he was known from then on.

Birbal comes from Bir Bar or Vir Var which means hazir jawab or quick thinker. Akbar gave titles to his Hindu subjects according to their traditions and S. H. Hodivala writes that it could have been taken from a character in the folk tale Vetala Panchvimshati. This featured a courtier called Vir Var who showed great loyalty to his king. Akbar was also fond of literature, having works of Sanskrit and other local languages translated into Persian.

His growing reputation led him to be part of Akbar's nine advisers, known as the Navaratna - the nine jewels. Birbal also played the role of a religious advisor, military figure and close friend of the Emperor, serving him for 30 years. In 1572, he was among a large army sent to aid Husain Quli Khan against an attack from the Akbar's brother, Hakim Mirza, which was his first military role. He later accompanied the Emperor during his Gujarat campaigns. Despite having no military background, he often participated in Akbar's campaigns and was given leadership positions, like Todar Mal, who was an advisor in economic matters.

Abu'l-Fazl ibn Mubarak and Abdul Qadir Badayuni were historians of the court. While Fazl respected him, listed him as having twenty-five honorific titles and rank of a commander of two thousand; Badayuni distrusted Birbal because he was a Hindu, calling him a "bastard" and in contempt, writing how he, as a Hindu musician, was getting favour and becoming the king's "confidant", but at the same time acknowledging his talent. Akbar's other orthodox Muslim advisers were known to dislike Birbal.