Who's This? He gets exactly one column on page 15 of Who's Who vol.I.
How you could have heard of him: In late 1999, an uncostumed Angle Man appeared in Flash #155. The character was then revamped in 2002 as, simply, Angelo Bend (from Wonder Woman vol.2 #178 on) and would go on to fight the Titans, Young Justice, Catwoman, Zatanna, and others. He's even appeared in the Justice League Unlimited and Brave and the Bold cartoons. But as of Who's Who vol.1, he only deserved a column, and famously, the smallest piece of art in the whole Directory.
Example story: Wonder Woman vol.1 #161 (1962) "Vengeance of the Angle Man!" by Robert Kanigher, Ross Andru and Mike Esposito
999,999 angles to go...
Who's Next? I'm honestly not sure... who have I missed that you really want to see done?