Who's This? The Quality hero on page 25 of Who's Who vol.XXVI.
How you could have heard of him: He appeared in a flashback in Animal Man #7 fighting the Red Mask. The Titans #36 makes him a friend of Liberty Belle's and turns him into a murderer. A female version of the character appears in Uncle Sam and the Freedom Fighters #3. Erik Larsen's Next Issue Project used him in its Crack Comics #63 (so did the character really slip into public domain?) and in Savage Dragon #140 in connection to that. However, his most substantial post-40s role has to be in James Robinson's The Golden Age, in which Lance Gallant is retired and resists his ghostly brother's urging to become Captain Triumph again. The mini-series isn't canon, but Robinson nevertheless used it in his Starman (#62 to be precise), where we're told Triumph was killed by the Mist.
Example story: Crack Comics #56 (1948) "Gossip Leads To Murder" by William Woolfolk and Reed Randall
Who's Next? Triumph was by no means the most obscure Captain in that issue of Who' Who...