The Grafted Blade Greatsword is the best weapon choice for a Strength-based build in Elden Ring.
While you need to make sure you invest in your Strength points first, you'll still need to have enough Dexterity points to ensure you can wield the Grafted Blade Greatsword.
Like the Bloodhound's Fang, the Grafted Blade Greatsword can be found relatively early in Elden Ring - even before you brave Stormveil Castle should you choose.
Grafted Blade Greatsword location in Elden Ring explained
The Grafted Blade Greatsword's location in Elden Ring can be found within Castle Morne in the Weeping Peninsula, which is south of Limgrave. This is can be found alongside the Irina quest, involving a young woman called Irina and her father Edgar.
You're actually looking to explore beyond the castle and further south, so you'll have to reach behind the castle (with a similarly named Site of Grace) and, just when it feels like you've reached a dead end on the outer wall, you can drop further down and eventually make your way to ground level on a beach where a boss awaits.
If you're just starting out, Leonine Misbegotten can be an intimidating boss, and possibly the first real challenge you face. On the other hand, if you arrive here later on, you'll make quick work of him. Once he's defeated, you'll be rewarded with the Grafted Blade Greatsword.
If you've been exploring other parts of the Lands Between and grinding your levels then you might be lucky enough to wield this weapon with a requirement of 40 Strength and 14 Dexterity.
Its unique skill, Oath of Vengeance, meanwhile, is a great buff temporarily raising all your attributes for a short time, while also increasing your poise.
Good luck finding the Grafted Blade Greatsword!