Leishman states the founding in his own words on River's about page: "I founded River in 2019 to build the bitcoin bank of the world." The same page carries the attribution "Alex Leishman, Founder, CEO & CTO at River" and lists him as chief executive on the team section.
The company record matches. River Financial Inc.'s Form D, filed with the Securities and Exchange Commission on 18 February 2021, gives 2019 as the year of incorporation and names Alexander Leishman as an executive officer and director, alongside Andrew Benson. That filing reported $17.3 million sold.
River is bitcoin only, and the positions Leishman has taken publicly through the company follow from that: published proof of reserves, published financials, and a product line that ends at withdrawal to a wallet the customer controls. He holds both the chief executive and chief technology officer titles, which is unusual at a regulated financial company and is stated here because it is what the company publishes.