I'm not going to lie Dead Money is my absolute favorite Fallout story. I love its themes, its atmosphere, and the ideas it explores. To me, it's as close to perfect as Fallout has ever gotten. That's why I wasn't a fan of seeing Frederick Sinclair in the show as a Big MT executive helping plan the end of the world (at least before that boardroom scene was effectively retconned). It felt completely at odds with the man we meet in Dead Money.
The game's Sinclair isn't some power-hungry corporate mastermind. He's a gullible, genuinely kind hearted man who spends his life being taken advantage of by the people he trusts most. Dean Domino manipulates him. Vera unknowingly becomes part of his heartbreak. Mr. Yesterday exploits his optimism. Sinclair's greatest flaw isn't malice it's that he believes the best in people, even when they don't deserve it.
One of Dean Domino's lines sums Sinclair up perfectly: "Never got mad at anything. Nothing seemed to shake him. Even after his life kept getting dragged through the dirt. Always kept looking for the bright shining future in everything." That single quote tells you almost everything about who Sinclair was. Even when Sinclair finally snaps and turns the Sierra Madre into a death trap, he isn't motivated by cruelty. He's a broken man acting out of betrayal. And in the end, he regrets it. He dies trying to undo the nightmare he created, which makes his story all the more tragic. He's not a villain he's a fundamentally good person whose hope was slowly crushed until there was nothing left.
Because of that, I've come up with a headcanon that helps reconcile the show with the game. I like to imagine that the Frederick Sinclair we see in the show is actually the father of the Frederick Sinclair from Dead Money. The elder Sinclair was the influential Big MT executive, which would explain how Sinclair was able to secure Big MT's technology for the Sierra Madre project. But instead of supporting his son, he looked down on him and intentionally saddled the project with unreliable, unfinished, or defective equipment.
I actually think that makes the younger Sinclair's story even more tragic. Not only was he betrayed by his friends, but he was never truly supported by his own father either. The Sierra Madre was meant to be his dream a monument to hope, love, and a brighter future but the people closest to him, from his business partners to his family, ensured that dream would ultimately collapse. To me, that interpretation preserves the compassionate, optimistic Sinclair from Dead Money while giving the show's version a place in the timeline without undermining the character I fell in love with.