Keith Shadis was the head instructor of the Military Training Corps. He was in charge of their training and evaluation to become soldiers. Keith was formerly the 12th Commander of the Survey Corps, being the direct predecessor of Erwin Smith, and the only Commander in the corps history to quit before death.
Keith was a tall and intimidating man. He was bald, with prominent wrinkles on his forehead and dark circles around his eyes. He had a small beard growing from under his chin. He was only ever seen wearing the standard instructor's uniform for the Training Corps.
In his youth, Keith was shown to be fascinated with the world beyond the Walls. It was this fascination that drove him to join the Survey Corps, and led to him developing a very self-righteous personality, often referring to himself as being "different" from everyone else within the Walls. This aspect of his personality was only strengthened after he met Grisha Yeager, whose high praise for Keith led him to begin considering himself a special "chosen" human being. Because of this, Keith started to look down on others, always considering himself the smartest person in any given situation, and he rejected new strategies from his soldiers as he felt his own ideas were adequate.
Appearance: Keith was a tall and intimidating man. He was bald, with prominent wrinkles on his forehead and dark circles around his eyes.
Personality: In his youth, Keith was shown to be fascinated with the world beyond the Walls. It was this fascination that drove him to join the Survey Corps, and led to him developing a very self-righteous personality, often referring to himself as being "different" from everyone else within the Walls.
History: Keith met Grisha Yeager in the year 832 outside of Wall Maria by the Shiganshina District. He encountered extremely few Titans that day.
Keith Shadis in the story: In the year 845, Keith leads an expedition outside of Wall Maria. Upon encountering a Titan, Keith orders the Survey Corps' attack groups to engage the Titan while he and the other soldiers act as decoys. As the corps returns to Shiganshina District after the expedition's failure, the mother of one of his fallen soldiers comes to Keith to inquire about her son.
Source: Attack on Titan Wiki, available under CC BY-SA 3.0.