One of The Umbrella Academy's biggest antagonists, the Handler, was an original character created just for the show, but the part was actually written for a surprising actor. The Handler, played by Kate Walsh, is a high-ranking member of the Temps Commission, the organization that oversees the management of the space-time continuum within the show's narrative. The Handler was mostly a behind-the-scenes player in The Umbrella Academy season 1 before becoming a more direct threat to the titular super-powered siblings in season 2.
With new antagonists in the form of the Sparrow Academy teased for season 3 and the Handler's story coming to a natural conclusion in season 2, Kate Walsh's turn as the character may well be over. However, given that she was a major player in the immensely powerful Temps Agency, it's not outside the realm of possibility that she may return in some capacity for future seasons. Regardless of whether or not the Handler will return, she was an integral part of The Umbrella Academy's seasons 1 and 2, and Kate Walsh put a distinct spin on the character that will be missed should her death prove permanent.
While Walsh was perfect in the role, the part of the Handler was originally written for someone very different. Speaking with Spotify's Behind The Scenes podcast, Walsh revealed that the part of The Umbrella Academy's villain was actually originally written with Jon Hamm in mind; it was only offered to her after he had passed on the role. The revelation changes a lot about the Handler, particularly with an eye to how Hamm would have tackled the role in comparison to Walsh's performance.
Kate Walsh's version of the Handler is defined by her unique sense of style, something which Walsh claims she was given plenty of creative input on. In contrast, Hamm's signature style is very clean-cut, and while he may well have brought the same sinister comedic quirkiness to the role in another sense, the Handler would have looked very different had he not passed on The Umbrella Academy. However, the Handler is interesting beyond just the character's outward appearance.
There's a theory that the Handler is one of the 43 super-powered kids in The Umbrella Academy, which goes some way towards proving the character's popularity, and that's something that Walsh personally delivered to the role. What's more, the Handler being a female villain brought a slightly different dimension to the character than Hamm would have been able to: as a man who is traditionally handsome with a distinctly clean-cut look, it's not hard to imagine Hamm's Handler as being far more generic a villain than Walsh's. While Hamm would undeniably have brought something special to the role, it would have changed the dynamic between the character and Five.
The chemistry between Aidan Gallagher's Five and The Umbrella Academy villain is part of what made season 2 so enjoyable. Had Kate Walsh not been offered the part - or if the Handler had been played by Jon Hamm - it may have all played out very differently. While Hamm would have worked in the role of a high-ranking Temps Commission co-ordinator, Walsh's unforgettable performance brought something special to the character, and The Umbrella Academy's seasons 1 and 2 wouldn't have been the same without her.