Grand Admiral Thrawn (Lars Mikkalesen)
In 1991, author Timothy Zahn revived Star Wars with his novel Heir to the Empire. It introduced one of the saga's greatest villains, Grand Admiral Thrawn. A brilliant blue-skinned alien Chiss, Thrawn was a master tactician who studied art to understand his opponents. He came close to leading a revived Empire against the New Republic before being killed.
The character would become massively popular and be featured in flashback novels. He made the jump to the Rebels series, showing his cunning. The series ended with Thrawn's ship dragged into deep space, thus explaining why he wasn't around during the original trilogy.
Now, Thrawn is back and ready to take the fight to what he still calls "The Rebellion." Given his genius, Thrawn is the biggest threat this galaxy has seen since the Emperor.
Ezra Bridger (Eman Esfandi)
A former thief, Ezra unlocked his potential for the Force when he joined the crew of the smuggler ship the Ghost. He was trained to become a Jedi himself and showed some great skill and drive as a leader. The Rebels series ended with Ezra helping take Thrawn to a distant galaxy and his friends planning to search for him.
So far, Ezra has popped up in the Ahsoka trailer in a holographic message. It's unsure what role he has to play in the series, but it will be exciting to see him back with his old crewmates and perhaps a full Jedi.