NOTE: This article is about the incarnation of Lash from the Marvel Cinematic film series. The mainstream version can be found here: Lash (Marvel Comics).
I am not merciful; I am necessary.
Now, you're free.
~ Lash's final words as he saves Daisy Johnson from Hive's control.
Professor Andrew Garner, also known as Lash, is a recurring character in the TV series Marvel's Agents of S.H.I.E.L.D., appearing as a minor protagonist in Season 2, a major antagonist in the first half of Season 3 while being an anti-hero in the second half, and a cameo character in Season 5's 100th episode.
He was the ex-husband of S.H.I.E.L.D. agent Melinda May as well as a former neurologist and forensic psychologist specialized in working with gifted individuals, before becoming an mutated Inhuman hunting down and killing his own kind.
In the aftermath of the worldwide Terrigen Mist outbreak, Garner's Inhuman genes activated when he was studying Jiaying's ledger, and he began hunting down and executing other Inhumans. Grant Ward, oblivious to the fact that Garner is Inhuman, had Werner von Strucker go undercover in one of his classes. When May and Hunter attacked Ward at one of his bases, he ordered Werner to execute Garner, who transformed to Lash during the assassination attempt and survived the subsequent explosion.
After Agent May found all of this out from Werner, she then confronted Andrew about the incident. Andrew snapped and accidentally shot her with an I.C.E.R., then took her to a hangar and explained how his transformation came about. However, Team Coulson, the A.T.C.U. and Lincoln found him and battled him. May shot him and he reverted to his human self. He was take into custody of Gideon Malick (a surviving HYDRA leader who Rosalind Price is secretly working with). During the attack on the HYDRA castle, he was freed by Jemma Simmons and defended her from several HYDRA soldiers that he killed, he also went on to murder all the Inhumans captured in stasis chambers and then escape.
Becoming Lash Permanently
Months after his escape and disappearance, Lash was captured by S.H.I.E.L.D., in which time he reverted back to human form. But, as Lincoln predicted before, Andrew states that when he next transforms, it will be permanent. Seeing how little time is left, Agent May went to Andrew's cell and the two talked about their former life and shared a connection. As Andrew was about to transform for the last time, May placed her hand on the window of his cell, and Andrew did the same, she tearfully watched as the man she loved changed irreversibly into the monster Lash.
Redemption and Death
As Glenn Talbot was ordered by Secretary Ross, he went to the S.H.I.E.L.D. headquarters to asses the Inhumans working there for the Sokovia accords. After meeting Elena and Lincoln, Talbot said "I've met the Good and the Bad, so now show me the Ugly". Phil Coulson then took him to Lash's cell, where Talbot was shocked as Coulson explained that he was what was left of Andrew Garner. During a staged escape plan used to trick Hive, who believed Lincoln was escaping, May placed Lash on a Quinjet and set it for Hive's location.When the Quinjet arrived, Hive patiently awaited Lincoln's arrival and saw the door opening. Then he looked on in shock as Lash stood behind it, who proceeded to attack Hive and through him off the launch pad. As the two fought, Lincoln explained every Inhuman has a purpose, and that Lash's is to kill Hive. Hive attempted to kill the monstrous Inhuman by unleashing his signature rapid-consuming cells from his hands, however Lash deflected it with energy blasts and continued fighting. Lash hit Hive in the chest with an energy blast, creating a large impact wound in Hive, who ordered his Primitive army to attack. Lash's hatred of Inhumans led him to kill all the attacking Primitives, before an enthralled Daisy Johnson attacked Lash with seismic activity, demanding the monster to stop. She collapsed due to blood loss from creating the Primitives and Lash went up to her and was able to remove her brainwash and carried her to the Quinjet. After setting her down Lash was attacked by Hellfire from behind, who through his fiery chain into Lash's back and dragged it back out, Daisy blasted Hellfire away with her powers as the Quinjet took off. Lash died having redeemed himself by saving Daisy.
This version of Lash highly differs from the comics, as Lash was the high priest from the hidden Inhuman city of Orollan, who sought to judge if Inhumans were worthy of their powers, and hunted down and executed those he deemed unworthy, as his culture deemed Terrigenesis a sacred gift.
It is noted that his Inhuman powers are supposed to fill a gap that exists. It's possible that Lash was meant to be Hive's killer, as he had the power to completely eliminate other beings.