Bitrefill's own funding announcement states that the company was "Founded in 2015, by Sergej Kotliar and co-founders Michael Grünberger and Michel Gustavsson". The company's press resources page carries interviews in which he appears as CEO. Its current about page uses the line "Trusted since 2014", so the company states its own start date two ways.
The work he is on record for is commercial rather than protocol. Bitrefill's account is that in 2017 it identified Lightning as the most viable route to scalable payments and made it a company focus, that it was first to market accepting Lightning, and that it is the largest commercial participant on the network. Those are the company's claims about itself. What followed was concrete: Thor and Thor Turbo in 2019, which sold inbound Lightning channel capacity to people who could otherwise not receive, and then ThorAPI so other platforms could open channels programmatically. Inbound liquidity was the practical obstacle to getting paid over Lightning at the time.
Only his public professional role is recorded here.