The man who has become the biggest thorn in Pru's side

In the spotlight: Robin Geffen

From his curriculum vitae, Robin Geffen looks a pillar of the City establishment, yet the founder of Neptune Investment Management has become the champion of the small shareholder in leading opposition to Prudential's $3.5bn (£2.4bn) takeover of the Asian insurer AIA.

Mr Geffen has more than 30 years of investment experience. He started his career at Charterhouse J Rothschild as a trainee after graduating from Keble College, Oxford. His career then took him to the insurer Eagle Star, York Trust and Scottish Equitable.

He set up Neptune Investment Management in 2002, having "identified a space in the market for a new, dynamic fund management firm that got back to basics and focused on delivering superior performance".

That sounds like PR spin, but investment specialist financial advisers say he can back it up. His funds had almost no banking shares in the run-up to the financial crisis and he avoided diving in too early when their shares looked cheap (but subsequently fell) in 2008.

Mr Geffen is a keen fisherman – his in-laws live on the River Test, a trout-fishing mecca, although he doesn't get time to go as often as he would like. He is too busy fishing for stocks and, while Neptune is becoming an increasing force, he still runs some of its flagship funds.

Retail investors, rather than City institutions, are his focus, so perhaps it is no surprise that he has been willing to lay bare some of the problems with Prudential's plans. With an action group now created, Prudential must take him seriously because he could yet put a planet-sized hole in its plans.