When Twitter was looking to raise $1bn from investors earlier this month, it put out the usual calls to Wall Street banks. The social media company also called Vijay Culas, who works out of rented office space on a busy stretch of highway in San Mateo, California.

A former Goldman Sachs banker who hung out a shingle in 2014, Culas helped Twitter negotiate with its banks and ultimately sell a type of hybrid bond for a 1% fee, one of the cheapest offerings in recent memory.