Krall, formerly Balthazar M. Edison, was a Human male who served in the United Earth Military Assault Command Operations and later the Federation Starfleet, until he was stranded on the planet Altamid. Edison became the brutal warlord Krall after the use of energy transference technology severely mutated his body.

Why does Krall change appearance?

Why did Krall/Edison's face keep changing? It looks like the alien machines he used to prolong his life (which he found on Altamid after the Franklin crashed there) gave him the appearance of whichever alien/aliens he absorbed life-force from.

What happened to Krall?

Sucked out into space, Krall was enveloped and disintegrated by the very bioweapon he planned to use on the inhabitants of Yorktown. Afterward, Kirk and Commodore Paris closed the file on Krall and the crew members of the USS Franklin.