By any measure, Wolverine is one of the most durable mutants on the X-Men's roster. While he's best known for his adamantium claws, his strongest power is his healing factor. While it usually helps him recover from flesh wounds and the occasional brutal physical battle, Logan's most impressive feat with his healing factor was regenerating an entirely new body from a single drop of blood.
In 1987's Uncanny X-Men Annual #11 by Chris Claremont, Alan Davis, Paul Neary, Glynis Oliver, Tom Orzechowski and Ann Nocenti. Wolverine accomplished this when his healing factor was given a massive power boost. The issue begins with Wolverine drunkenly stumbling back to the X-Mansion and being greeted by the recently awakened X-Men. While Logan knelt in front of the altar he'd set up for his lost love Mariko, the X-Men were attacked by the alien warlord Horde. The team tried to defeat him but found their attacks didn't hurt him. Knowing they couldn't defeat him, the X-Men conceded to Horde's request that they travel to the Citadel of Light and Shadow to retrieve the Crystal of Ultimate Vision.
At the Citadel, every member of the team faced illusions of their most powerful desires. Rogue saw herself as the center of attention at a fanciful ball. Meanwhile, Havok became a literal star as he released his powers. One by one, the X-Men were sucked into the illusions and transformed into statues until only Psylocke, Storm and Wolverine were able to escape their illusions. In a bid to stop Horde, Psylocke sacrificed herself. Wolverine, realizing his adamantium bones and healing factor would give him the best chance to defeat Horde, pushed Storm back into her illusion.
Alone with Horde, Wolverine rushed towards the Crystal of Ultimate Visions but his rush was cut short when Horde threw a spear through Wolverine's back. Feeling victorious, Horde pushed his clawed hand through Wolverine's chest and took out his heart, functionally killing him. Unbeknownst to Horde, a single drop of Wolverine's blood landed on the Crystal and functionally supercharged his healing factor, allowing him to regenerate his entire body in seconds. Wolverine explained to Horde that his healing factor, and therefore, his will to live inhabited every cell in his body. The Crystal also gave Wolverine cosmic powers which he uses to defeat Horde and destroy the Crystal, sending him and the rest of the X-Men back to the mansion as if they hadn't been hurt at all.
Since Logan is a relatively grounded hero, this kind of cosmic power is far beyond what Wolverine usually has at his disposal. But just as it is in his more grounded adventures, Wolverine's greatest advantage is his healing factor. That mutant power turned Wolverine's blood into a medical miracle, making him impervious to any type of infection or cancer and capable of repairing grievous wounds in moments. But here, Wolverine's blood became something far more than that, it became the very embodiment of his scrappy spirit, and it facilitated his rebirth, complete with adamantium claws.
Wolverine's always called the best there is at what he does, and his healing factor plays an essential role in making that a reality, On most days, it allows him to take unbelievable amounts of damage and shrug it off like it was only a scrape. But in its overcharged state here, it became a tangible symbol of his indomitable will to survive.