His policies were comparable to, and sometimes to the right of, those of the SDP. The SDP being the right of the Labour party who split in the 1980s and later merged with the Liberals to give today's LibDems.
He was more of the fringe in his youth. So were quite a lot of people, current politicians, even Blairites included. Peter Hain (anti-apartheid and gay rights) and David Blunkett (Socialist Republic of South Yorkshire[0]) spring to mind as having had far more activist and strident roots than Corbyn. Blunkett went on to be a Home Secretary the right of the Tory party would have been proud of.
Edit: Nowhere am I advocating his policies, why the downvotes?
[0] https://en.wikipedia.org/wiki/Socialist_Republic_of_South_Yo...