The Umbrella Academy removes an important part of Luther's comic book design - and he's much harder to sympathize with as a result. Under the guardianship (using that term very loosely) of Sir Reginald Hargreeves, the young siblings of the Umbrella Academy all suffered in one way or another. Vanya was drugged, Klaus became traumatized, Diego got angry, Five went missing and Ben died - not exactly a fantastic parental record. Despite being the Academy's noble leader, even Luther couldn't escape the pattern of misery. Born with enhanced strength, Luther was gravely injured during a mission, forcing Reginald to revive him using a mysterious gorilla serum. Though his life was spared, Luther's body took on the appearance of an ape.
Naturally, this unwanted physical transformation became a source of pain for Luther. The hair-covered primate torso serves as a constant reminder of the price Luther paid as Sir Reginald's only loyal child, and alienates him even further from the other Hargreeves kids. Luther's animalistic appearance has also destroyed his confidence. When Luther and Allison were growing close as teens, he possessed a certain swagger as Reginald's "Number One." In the present, Luther has all but given up on Allison - partly because he believes no one can love that carpeted, ape-like chest.
However, Netflix's The Umbrella Academy makes an all-important alteration to Luther compared to the original comic books by Gerard Way and Gabriel Bá. In the source material, Luther's head is grafted onto the body of a giant alien ape. Spaceboy has no choice but to parade around topless, his physical alterations on display for the entire world. Tom Hopper, on the other hand, merely pops on an XXXL shirt, and his deformities are covered. Most of the time, Netflix's Luther looks like a very big man, not the subject of a dangerous and experimental scientific procedure that fundamentally rewrote his DNA. From a behind-the-scenes point of view, The Umbrella Academy's Luther change is completely understandable - having one of the main cast constantly wearing the upper half of gorilla sounds expensive, impractical, and probably wouldn't translate well into live-action.
But constantly obscuring Luther's physical differences with over-sized pastel shirts also makes the character harder to feel sorry for. In the comic books, readers are reminded of Luther's accident with each and every panel he appears in. On TV, it's more like "out of sight, out of mind." Since Luther looks relatively normal 95% of the time (like he went way too hard at the gym), it's easy for the audience to lose sight of why he's hurting. For other characters, the emotional scars are clear and constant; Klaus' addiction is always apparent, and Ben's spectral form is a sure sign that he's still dead. But when Luther does occasionally strip off, there's still that moment of shock and realization where the viewer remembers his whole gorilla ordeal, and are reminded of what Number One lost as a member of the Umbrella Academy.
Luther wearing shirts isn't the reason so many The Umbrella Academy viewers have failed to empathize with the character... but it certainly hasn't helped. After The Umbrella Academy season 1, somewhat of an anti-Luther movement began, with fans believing his controlling personality and toxic behavior was instrumental in Vanya triggering the apocalypse. Perhaps the Luther haters might've been more inclined to cut Spaceboy some slack if his physical aberrations were constantly in view. After all, it's the tragedy of his accident that (partially) causes the personality faults Luther's detractors so keenly point out.