This is what the SSP website says about him:-
Colin Fox has been convenor of the SSP since February 2005 with a 20 year record of activism in the socialist and trade union movement.
Colin has spoken out repeatedly on the appalling situation in Scotland’s prisons and has challenged the Scottish Executive on it’s simplistic Anti Social Behaviour legislation.
Colin co-organises the Edinburgh Mayday Festival and founded the Edinburgh People’s Festival in 2002.
Formerly a Labour Party Young Socialist, Colin returned to Scotland as an organiser for Scottish Militant Labour, playing a key role in bringing together the Scottish Socialist Alliance in Edinburgh and then became a founder member of the SSP.
Scottish Parliament web-page for Colin Fox
We chatted to him last year when he was standing for Holyrood and you can read that article here.