Marshall D. Teach, also known as Blackbeard, is one of the notorious figures in the world of One Piece and has become a significant adversary to the World Government. Before he became one of the most powerful characters in One Piece, he was merely an unnamed figure embarking on his journey shortly after joining the Whitebeard Pirates.
To date, despite the publication of over a thousand chapters of One Piece, there is still very little information about Blackbeard, making this character even more enigmatic. However, it is highly possible that creator Eiichiro Oda is hinting at something special regarding this character through the number “3”.
At first glance, there seems to be no direct connection between Blackbeard and the number 3, but when we analyze the details and delve deeper into the character, everything becomes clearer.

For example, the emblem on Blackbeard’s Jolly Roger flag features three skulls. Notably, he also carries three pistols and is often seen with three tattoos. Moreover, the number 3 could also imply that he possesses up to three Devil Fruits from the Paramecia, Logia, and Zoan categories.
Currently, Blackbeard has two Devil Fruits: Yami Yami no Mi from the Logia category and Gura Gura no Mi from the Paramecia category, both obtained from Whitebeard. Therefore, the last fruit he possesses might eventually be a Zoan-type Devil Fruit. However, this aspect has yet to be clarified, but it is quite possible that Blackbeard has consumed three Devil Fruits in total.

As you may know, Oda has utilized numerous figures from Greek mythology in his works, so we can certainly hope that the author has chosen a character from Greek mythology for the “ultimate upgrade” of Blackbeard.
Among the Greek mythological figures that might relate to Blackbeard, Poseidon stands out the most (notably, there is a character named Poseidon in One Piece as well). Poseidon is the god of the sea, known for his ability to control both the ocean and earthquakes, and is regarded as a powerful deity, second only to Zeus. These aspects are closely related to Blackbeard.
Both Blackbeard and Poseidon possess the ability to create earthquakes and have connections to Medusa and Pegasus. In Chapter 1063 of One Piece, Blackbeard is seen confronting Stronger – a creature that has consumed the Uma Uma no Mi, Model: Pegasus. Furthermore, Blackbeard has previously attempted to capture Boa Hancock – a woman with the power to turn others into stone. Additionally, Poseidon’s “dark shadow” is echoed in Blackbeard’s connection with the number 3, where the powers of Poseidon can be represented by a trident.
Moreover, the unique downside of the Devil Fruits is that their powers are limited by the ocean, and those who possess these powers cannot swim. Additionally, the user of the Devil Fruit also cannot know their true potential.
However, if Blackbeard were to consume the Hito Hito no Mi, Model: Poseidon, we could see a significant transformation, allowing him to cross the limitations of an ordinary person compared to the Devil Fruit user.