Vtyjkyuk

I think you are

Mount Everest, or Chomolungma

I am a triumph, a thundering wall; a goddess, a ruler the grandest of all.

Largest mountain in the world, and reaches to the clouds. Miyolangsangma is the Tibetan goddess of Giving who is said to live at the top of Everest. Alternatively, it may refer to Everest's Tibetan name, Chomolungma, which means Goddess Mother of Mountains. (@El-Guest for the name)

I loom over towers that can touch the skies; few of world's waters can rival my size.

As above. Everest is ~29 thousand feet above sea level, and the average ocean depth is ~12 thousand feet below.

A landmass colossal, a forebear of kings; on seven continents my name still rings.

It's a mountain all right, and has been there a long time. People from all over the world come to Everest to conquer it.

I think that it is

"mother nature" because it says goddess and all of the other phrases kind of match. Nature has mountains and other natural landforms. Again, natural landforms. A lot of people call nature mother nature and that is the name too. (going along the riddles lines like @sensoray suggested)

My guess is that you are

Pangaea, a supercontinent that broke up about 175 million years ago.

I am a triumph, a thundering wall;

a goddess, a ruler the grandest of all.

Pangaea is the largest of continents. Perhaps "thundering wall" refers to the collision of tectonic plates that formed Pangaea. It is named for the goddess Gaea, Mother Earth in Greek mythology.

I loom over towers that can touch the skies;

few of world's waters can rival my size.

Pangaea covered a huge area and contained many impressive mountain ranges.

A landmass colossal, a forebear of kings;

on seven continents my name still rings.

I'm not entirely sure of this one but I think it refers that the current seven continents are made up of the pieces of Pangaea after it broke apart. The reference to kings might mean the current seven continents or perhaps Laurasia and Gondwana two later supercontinents that formed in between the time of Pangaea and our current configuration.

Could the answer be

Seven 7?

I am a triumph, a thundering wall;

The word triumph has seven letters, and there are seven famous border walls

a goddess, a ruler the grandest of all.

Again, the word goddess has seven letters, and there are seven olympian goddesses (with six shown in the link, and then Iris as their messenger and Goddess of the Rainbow).

I loom over towers that can touch the skies;

Unsure about this one. But...

...it could possibly refer to the seven heavens which talks about "the seven layers of the sky" and the "seven planets in our solar system". However, science reveals that there are five layers of the atmosphere (sky); and there are 9 planets in our solar system thus far, though there may be 12 planets.

Vesta was a planet, then reclassified as an asteroid; Eris is now classified as the most massive dwarf planet in our solar system (thus far), though that is not an actual planet, just like Pluto; but we do have the so-called Planet Nine (and then "the mysterious, mythical Nibiru (Planet X) which apparently 'destroyed life on the red planet, Mars'..." but let's not get into that).

few of world's waters can rival my size.

The seven seas, whatever they were, really. There are many references with different kinds of seas, but there are seven main oceans.
_{In the former link, the term "yesteryear" means "last year".}

A landmass colossal, a forebear of kings;

The seven wonders of the ancient world and/or the seven wonders of the modern world.

on seven continents, my name still rings.

The seven continents and how in the centre of all of them, there is the Ring of Fire. (There is some debate that there should be eight continents, but that debate is pretty much comparable to the debate on whether or not Pluto is a planet.)

What is my name?

Seven?

Title:

A humble riddle

The Seven Virtues, whichever set you probably referred to in the title (although Aristotle argues that there are twelve, pursuant to his 'Golden Mean' of actions regarding Nicomachean Ethics.)

_{The links I chose in my answer are just the simplest links with not as much information compared to other sites, because at the end of the day, this is just a riddle we are talking about.}