On page 37 of Ulysses, James Joyce uses the phrase "Los Demiurgos."

Los

At first glance, the word "Los" seems to be the definite article for "Demiurgos."

However, it could also refer to Los, a character in the mythology of William Blake. See, for instance, the poet's The Book of Los.

(Blake's mythology also appears in the poet's Milton: A Poem in 2 Books, which Joyce references with the phrase "Am I walking into eternity along Sandymount strand?")

According to William Blake's mythology, the primeval man, Albion, was split into four separate beings (which Blake called "Zoas") after The Fall.

The first Zoa is Tharmas, which represents instinct, nature, and unity.

The second Zoa is Urizen, which represents laws, culture, and conventional reason, and resembles the Gnostic concept of the Demiurge.

The third Zoa is Luvah, which represents love, passion, and rebellious energy. In his "fallen form," Luvah is called Orc.

The fourth Zoa is Urthona, which represents creativity and inspiration. In his "fallen form," Urthona is call Los.

In Blake's artwork, Los is often depicted as a smith with a hammer to represent the beating of the human heart (which might explain Joyce's phrase "made by the mallet of Los").

One of Blake's most complete description of his mythology can be found in the unpublished epic poem, Four Zoas: The Death and Judgment of Albion The Ancient Man.

A breakdown of the key characters in Blake’s mythology can be found here.

Demiurgos

“Demiurgos” is Spanish/Portuguese for the Gnostic concept o the Demiurge.

Joyce uses this form of the word to complete the multilingual pun started with “Los.”

It also happens to resemble the ancient Greek (that is, the original) form of the word.