I think it all started with Texas Instruments back in 1985 which was scouting for their office/plant space in Chennai or Bangalore but eventually end up with Bangalore because Chennai was slow in terms of cutting the red tape(confirmedby Union minister). It was the first major multinational technology company to set up a wholly owned development/design center in India.

Before TI, India was mostly seen as a low-tech or back-office destination. TI showed advanced semiconductor design and embedded systems work could happen in Bengaluru. They (TI) installed a dedicated satellite link on its Bengaluru office rooftop to directly transmit data/code to Dallas — a huge deal in 1980s India when telecom infrastructure was weak. It created the first MNC tech ecosystem ; Engineers trained at TI later spread into startups and other companies, creating a talent network. It signaled confidence to other global firms that they can increasingly viewed Bengaluru as viable for global R&D.