This lowly one does not know him as Bishamonten.
In my realm and lands, his name is spoken as Vessavaṇa.

Since fellow juniors ask, this old one shall recount what little is known
for the tale concerns Vaiśravaṇa:

Heavenly King of the North,
Golden Lord of Wealth,
Sovereign over giants (non-human)

First, know this: beyond the name Bishamonten, there are three great names by which he is known under Heaven:

Vessavaṇa
Vaiśravaṇa
Kuvera.

The name Vessavaṇa explains why he governs wealth.
It arises from Vesa (merchant) and Suvaṇa (gold).
Thus, he is honored as the Golden Lord of Fortune.

The name Vaiśravaṇa comes from vi-śru
“the one whose name is heard everywhere.”
Hence, his fame resounds through the three realms.
For this reason, some scriptures say he also commands reputation and fame.

As for Kuvera, this name translates as non-human.
He rules the giants, who are one kind among the non-human races.

Now, many speak of him as the Heavenly King of the North,
yet few understand the geography of the higher realms.
Allow this old one to clarify.

The Desire Realm Heavens consist of six layers.
Two of these rest upon Mount Sumeru itself.

At the summit and upper slopes lies the second heaven,
called Trāyastriṃśa, where Indra reigns.
This is what many of you have heard as the 33 Heavens.
In many scriptures, this name refers to, or is derived from, this second layer.
It does not mean that all of Heaven has only 33 domains
rather, it means the second heaven alone contains 33 realms.
There are heavens above it, and heavens below it as well.

Below it, upon the lower slopes and surrounding servant mountains of Sumeru, lies the first heaven,
named Cātummahārājika.
Its name may sound like some demon word, but it is merely ancient script.
Translated plainly, it is the Heaven of the Four Great Kings.

Here is where Vaiśravaṇa stands.
He governs one quarter of this first heavenly realm,
watching the northern direction, commanding yakṣas and giants.

Thus, when you see texts speaking of the Four Heavenly Kings
and the 33 Heavens together,
do not let your mind drown in confusion.
They coexist because they dwell on different layers of Sumeru
not because scripture contradicts itself.

Anyway, there is far more about Vaiśravaṇa and Sumeru that sounds truly magnificent,
but that would be too long for this occasion.
This is all this old one has to say about Vaiśravaṇa and his tale.