The Jedi Master known to history as the bounty hunter Sutrejn De'eva survived Order 66 because he was undercover at the time, and he kept to his cover for the remainder of his life.
Biography
Birth and early years
"Sutrejn"'s birth-name has been forgotten, and the name "Sutrejn" is not referenced in any surviving records of the Jedi Order - at least, not as a Jedi. The De'evan family was in the ascendancy once again, producing non-combat droids.
Training
"Sutrejn" trained as a Jedi Sentinel, and he was knighted long enough before the beginning of the Clone Wars that he managed to train his first Padawan, achieving the rank of Jedi Master several years before the Battle of Geonosis.
The Clone Wars
Jedi Master "Sutrejn" De'eva did not openly participate in any major battles during the Clone Wars. Instead, he spent the majority of the war behind enemy lines attempting to discover what really lay behind the Separatist movement. It is believed that he discovered some corroborating evidence of Darth Sidious' existence, though he did not discover the Darth's identity before the Darth revealed it with his Proclamation of a New Order.
Order 66
At the time that the newly self-declared Emperor Palpatine issued Order 66, "Sutrejn" was undercover as a bounty hunter investigating rumors of a Sith having been seen in Mandalorian space. After learning of the fall of the Republic and the rise of the Galactic Empire, he, with the aid of contacts among the Mandalorians, faked his own death, taking on his disguise as the bounty hunter Sutrejn permanently. He later claimed the bounty on his own head.
Age of the Empire
While Sutrejn didn't manage to escape the notice of the Inquisitorious, he did manage to convince them that his Force sensitivity was marginal at best through deliberately hiding it. He also held a good record hunting down pirates plaguing the hyperlanes, and he turned in several bounties on Jedi over the course of his bounty hunting career - one of whom he actually took on as his Padawan after a duel which should have killed her (and, in fact, almost did.) What the Inquisitors did not know was that most of the Jedi he fought actually escaped alive - minus their lightsabers - and those who did not tended to actually be Dark Jedi.
Sutrejn eventually married another gray Jedi, who bore him a son and a daughter. His son became his third Padawan once he was old enough - by which time the Jedi Master had knighted his second Padawan.
Death
Sutrejn De'eva was eventually killed in a space battle with pirates in the Outer Rim, along with his entire crew. His wife and teenage children survived in hiding, though his son ended up leaving home to journey to Moraband as the beginning of what would become a more than five decades long quest to find the holocron of his distant ancestor, Lord Kaissen De'eva. The young Jedi was there seduced to the Dark side, seemingly destroying his father's legacy in the process.
Skills and powers
During his time as a Jedi prior to the Clone Wars, "Sutrejn" specialized in disguise and infiltration, though he also extensively studied Mechu-deru despite the Jedi Order's abhorrence for it. He was capable of guiding a ship through hyperspace and of re-programming droids on the fly. He re-built two magna-guards and trained them to guard his personal starship and aid him in boarding actions as needed. They would later assist him in training his second Padawan.
Lightsaber combat skills
"Sutrejn" used primarily Form V lightsaber combat tactics, though he also definitely had training in Form IV, Form III, and at least some knowledge of Form VI and Form I. He wielded a single-bladed lightsaber of an ancient design, with a magenta core and a purple blade. He continued to carry this lightsaber even after the execution of Order 66, justifying his possession of it by faking his own death with the aid of contacts among the Mandalorians, then claiming the bounty on his own head.
Behind the scenes
Vatharn invented Sutrejn De'eva as part of the backstory for The De'evan project to help explain how Darth Nikkan De'eva could give the impetus for a later Sith to seek Lord Kaissen De'eva's four-thousand years old holocron.