Squad 666 (nicknamed Reaper) is a special operations team of SPARTANs who specialize in stealth and infiltration. Squad 666 is led by Rachel-053, and is a splinter faction of Squad 596.
Rachel-053 - Team leader
Darman-A136 - Second in command, CQB specialist, marksman
Andrew-125 - Medic, Pilot
Rachel is the first in command of Squad 666. she was born on Earth. Not much is known about her, except for that she was born in 2511, and after augmentation, was put in a cryo-sleep when not needed, preventing her from physically aging. After the Human-Covenant War, Rachel was used for stealth and close quarters in urban areas. she then was put in Squad 596, but was believed to be killed by her team mates. However, a splinter squad of Squad 596 was created for specialized missions in which a small team specializing in stealth would be necessary, called Squad 666. Rachel was made the commander of this team.
Darman-A136 is a SPARTAN-III and Second in command on the team. His record states that he was born February 15th, 2522 on [location not listed]. Not much else is known about him at the time.
Andrew-125 is a SPARTAN-II who's team was killed two months before he was transferred. ONI put him in cryo-sleep for the two months after his team dies to when he was transferred in.