Secret 12:
Who is Alex Krycek?

Fondly known as "Ratboy" on the Internet, Alex Krycek is a renegade FBI agent who appears to be on the side of the Syndicate and the shape-shifting aliens.

He has clashed with Mulder many times (and is the only person Mulder seems able to beat up).

Speaks fluent Russian, has one arm (the other one was cut off by Russians who knew he was on the side of those experimenting with the black oil).