The fastest character in DC

Wally West   Traditionally, and in most comic storylines, Wally West holds the title of "The Fastest Man Alive." 

Barry Allen  Barry Allen, the original Flash, was also known for his incredible speed, often reaching near-light velocities using the Speed Force.  

Black Flash:  This mysterious entity serves as the "Grim Reaper" for speedsters, residing outside the Speed Force and tasked with capturing those who escape their natural lifespans.  

Lightray   Earth 9's Flash in the DC multiverse, Lightray is not a speedster in the traditional sense.