The celebrated and wise planeswalker Teferi made his initial appearance in card names and flavor text way back in Mirage, in cards like Teferi's Imp, Teferi's Curse and Reality Ripple. He was referenced lightly during Urza block (Stern Proctor, Disruptive Student) and once in Masques block (just Excavation as far as we can tell), but he didn't show up in earnest in Magic art until Invasion.
In that set, Teferi was depicted with a characteristic robe, headdress and staff. Check it out:
ExcludeTeferi's CareTeferi's Moat
Note how Teferi holds back those bad guys above. Can you tell what group that's supposed to be across the moat? Here's a hint.
You can also see Teferi on Disrupt and Teferi's Response, among others. (Teferi also made a Teferi's Puzzle Box once. Look, a Puzzle Week tie-in!)