Who's This? The Viking who is also a Commando on page 12 of Who's Who vol.XXV.
How you could have heard of him: Beyond Who's Who and History of the DC Universe, there hasn't been any call to even see Viking Commando since the Crisis. For shame.
Example story: All-Out War #2 (1979) "No Miracles -- No Survivors!" by Robert Kanigher and George Evans
Who's Next? A villain comes forward. He looks legit. Was probably around all the time in the Silver Age. Uhm, no. You wouldn't believe how few appearances he's made.