You've played Resident Evil 2. You’ve seen the horror. But there is something genuinely upsetting about the way William Birkin ends up. It’s not just "boss fight #5." It’s a total biological collapse. By the time you reach that train platform, the man—the genius scientist who wanted to be a god—is basically a sentient puddle of meat and teeth.
Honestly, it’s kinda tragic. Birkin didn't just die; his own creation ate him from the inside out until there wasn't even a skeleton left to hold him up.
The Science of a Biological Train Wreck
Most players think the G-Virus is just a "stronger" version of the T-Virus. That's wrong. While the T-Virus creates stable (if ugly) bio-weapons like the Tyrant, the Golgotha Virus is pure, unbridled evolution. It never stops. Every time Birkin took damage, the virus panicked and "fixed" him by adding more biomass.
By the time we see the William Birkin final form, known as G5, he’s no longer a humanoid. He’s a "G-Creature" that has lost all structural integrity.
Think about it. In the first few stages, he has a pipe. He has a face. He has a plan (mostly just "find Sherry and reproduce"). But G5? G5 is what happens when you hit the "fast-forward" button on evolution and the machine breaks. He's a massive, pulsating wall of flesh filling an entire train car.
What Really Happened with the G5 Mutation?
In the original 1998 classic, G5 was a bit more of a "blob with tentacles." The 2019 remake turned the nightmare up to eleven.
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The Physical Breakdown
In this state, Birkin has essentially become a mollusk. His bones have likely softened or dissolved entirely to allow him to fit into the narrow spaces of the Umbrella transport train. You can still see vestiges of his former forms—the giant claws are now just fleshy protrusions, and the hundreds of smaller eyes from G4 have merged into one massive, central "G-Eye" inside a cavernous mouth.
Is William Still In There?
This is the part that haunts lore nerds. In the Darkside Chronicles, there’s a hint that he might still be conscious on some level because he screams "Sherry!" during the fight. But realistically? Most experts agree Birkin "died" somewhere around Stage 2 or 3. By the final form, the human brain has been shifted, compressed, and likely replaced by a primitive "G-Brain" that only cares about one thing: consuming biomass to stay alive.
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It’s just instinct. Pure, raw hunger.
Surviving the Final Encounter
If you’re staring down this wall of teeth on the train, you’re probably low on ammo. That’s the Resident Evil way. But the William Birkin final form is actually a bit of a "gear check" rather than a complex tactical dance.
- The Eye is Everything: Don't waste bullets on the fleshy bits. G5 only takes real damage when that massive central eye opens up.
- Distance is a Myth: The train car is small. He’s going to keep sliding toward you. In the remake, it’s a race against time. If he reaches you, it’s an instant game over. No "Caution" or "Danger" state—just a very messy snack for the G-Virus.
- The "Kitchen Sink" Strategy: This is where you dump every remaining grenade, spark shot, and magnum round. If you’re playing as Leon, the flamethrower is surprisingly effective here because the DOT (damage over time) keeps ticking even when the eye is partially obscured.
Why G5 Still Matters in Gaming History
We see a lot of big monsters in games. Huge dragons, giant robots—whatever. But Birkin’s final form represents a specific kind of body horror that sticks with you. It’s the visual representation of "too much of a good thing."
Birkin wanted immortality. He got it. But he’s immortal as a heap of sludge that can’t even remember his own name. It’s a cautionary tale wrapped in a survival horror boss fight.
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Misconceptions to Clear Up
- G5 isn't the "peak" of the virus: It's actually a sign of failure. The G-Virus was supposed to create "G-Humans"—stable, evolved supermen. Because Birkin was wounded when he injected himself, the virus was forced to adapt too quickly to trauma, leading to these unstable, bloated forms.
- The train explosion killed it, not the bullets: You’re just slowing it down. The only reason G5 is gone for good is that the entire train went up in a tactical explosion. Without that, it probably would have just kept growing, eventually filling the entire tunnel system.
To truly understand the horror of the G-Virus, you have to look past the gore. It’s about the loss of identity. By the time you’re looking at the William Birkin final form, you aren't looking at a man anymore. You’re looking at a biological accident that doesn't know how to stop existing.
If you're looking to master the lore, your next step should be diving into the "Report on the G-Virus" files found in the NEST laboratory. They detail exactly how Birkin's DNA was rewritten and why Sherry was the only hope for a "stable" version of his legacy. Understanding the "G-Human" concept vs. the "G-Creature" disaster makes that final fight feel a lot more significant than just a race against a timer.