The first Indian ruler to be shown in images as wearing a dress akin to trousers is

Kanishka, the most prominent ruler of the Kushana Empire, is the first Indian ruler depicted in iconography wearing a dress akin to trousers. This distinct attire, often referred to as Central Asian or Scythian dress, typically included a heavy long coat and quilted trousers, reflecting the Kushanas' nomadic origins from the steppes [4]. The most famous representation is the headless statue of Kanishka found at Mat, near Mathura, which clearly shows him wearing these trousers and heavy boots [5]. This style of dress was a significant departure from the traditional Indian dhoti worn by earlier Mauryan rulers like Ashoka or Chandragupta. While later Gupta rulers like Samudragupta also adopted similar attire on their coinage, Kanishka remains the earliest major ruler to be systematically depicted in this fashion due to the strong Central Asian influence during the Kushana period [4].

Sources

1. [1] History , class XI (Tamilnadu state board 2024 ed.) > Chapter 6: Polity and Society in Post-Mauryan Period > Kanishka > p. 80
2. [4] History , class XI (Tamilnadu state board 2024 ed.) > Chapter 4: Emergence of State and Empire > Introduction > p. 46
3. [5] History , class XI (Tamilnadu state board 2024 ed.) > Chapter 7: The Guptas > 7.3 Chandragupta II > p. 92
4. [2] https://en.wikipedia.org/wiki/Art_of_Mathura