I've been playing thus far that his part in the formation of the Rebel Alliance (as in, he started it under Vader's orders to gather rebels to distract the Emperor) was kept a secret by it's founding members, since he was a Sith that turned traitor. That's why no one knows who he is. Otherwise we're fudging the Legends/Canon divide a little XD

But yes. ALL of the friends, especially for Galen :-D