William Jones (18 September 1745 - 27 April 1794) was a British orientalist and became a judge in India. He realized that India has a lot to offer in the meanings of sciences and arts, and certainly has benefited from it. He translated the Laws of Manu (Manumriti) to English and then, many other works of literature; was the first western to study and write a paper on Indian Classical Music, etc. There's no doubt that he was a man of a brilliant mind considering all those conquests. But he is most acknowledged by proposing that  Sanskrit, classical Greek, and Latin shared a language root in common. Lately, this root was named "Proto-Indo-European". The discovery popularized the comparative linguistics (If you want to know what is comparative linguistics, click here), which led to new theories, techniques, and studies of the Proto-Indo-European languages. 

source: Navrang India

Thanks to his initiative, today we have the Kurgan hypothesis, that proposes that the Proto-Indo-European lived in the Pontic-Caspian steppe of Eastern Europe in the 4th millennium BC. Their language probably split into different languages around 3.500 BC, when they expanded from their original settlement into different parts of Europe and Asia (Jana, 2014). However, in the 20th century, historical linguists discovered the Anatolian and Tocharian languages, which led to a change in some linguistics features and to the acceptance of the Laryngeal Theory (laryngeal consonants that later disappeared from all Indo-European languages except the Anatolian). There are many other possible relationships, but they remain controversial. This lack of pieces of the puzzle persists because there are no written records of Proto-Indo-European, that is the reason why the scientists use methods as reconstruction, comparative, and works with some hypothesis. 

Here is the main division of Indo-European languages (Anthony, 2007):

• 1. Anatolian (4200 BC, Asia Menor, extinct)
• 2. Tocharian (3700 BC, China, extinct). 
• 3. Germanic (3300 BC, earliest runic inscriptions from around the 2nd century AD, earliest coherent texts - as the translation of the Bible into gothic by Wulfila). Old English manuscript tradition from about the 8th century AD. Many contributions).
• 4. Italic (including Latin and the romances languages, 3000 BC)
• 5. Celtic (3000 BC)
• 6. Armenian (2800 BC)
• 7. Balto-Slavic (2800 BC)
• 8. Hellenic (2500 BC)
• 9. Indo-Iranian (2200 BC)
• 10. Albanian (attested from the 14th century AD).

There are many other Indo-European languages, but they are all extinct and the knowledge that we already have is limited due to the lack of information and contributions. 

The information above was taken from:

PROTO-INDO-EUROPEAN. In: CHAMONIKOLASOVÁ, Jana. A Concise History of English. Masarykova Univerzita: [s. n.], 2014. cap. 2, p. 7-15. ISBN 978-80-210-7480-4. Disponível em: https://digilib.phil.muni.cz/data/handle/11222.digilib/131572/monography.pdf. Acesso em: 18 set. 2020.

"Sir William Jones who made the ancient language Sanskrit known world over – British India", Navrangin India, (September 18, 2020).

"Biography of Sir William Jones". Kamat’s Potpourri - The History, Mystery and Diversity of India, (September 18, 2020).

"Sir William Jones". 1911 Encyclopedia, (September 18, 2020).