Ἄτλας κρατερόφρων → stout-hearted Atlas

[Mark Manguno]

Hello! I know nothing at all about Ancient Greek, so I'd like some help here.  I just had a son who we named Atlas, and I would like to figure out how to express the noun phrase above, from Hesiod, in the nominative, as opposed to what I think is the accusative?

Accusative?: Ἄτλαντα κρατερόφρονα
Nominative: Ἄτλᾱς ... ?

κρατερόφρων seems to be κρατερός (pretty sure this is the nominative) + the suffix -φρων, which is the "o-grade" of φρήν but I have no idea what "o-grade" means, nor can I figure out how adding a stem of this sort would affect the declension.  Any help would be greatly appreciated! Thanks!

[spiros]

Ἄτλας κρατερόφρων

Not sure what you find confusing, κρατερόφρων is a compound word with its own forms.
κρατερόφρων - Ancient Greek (LSJ)
Hesiod,  Theogony, line 507

The -o- bit is a way to join two words into a new one.

A linking vowel inserted interconsonantally between two morphemes, to ease pronunciation, without contributing to the meaning. It frequently joins words or combining forms of Ancient Greek or Classical Latin origin in the classical compounds of New Latin and international scientific vocabulary, but it can also be used to join modern terms and even abbreviations, either formally or informally.
-o- - Wiktionary

ὁ κρατερόφρων      
τοῦ κρατερόφρονος   
τῷ κρατερόφρονι   
τόν κρατερόφρονα   
(ὦ) κρατερόφρον   
οἱ κρατερόφρονες             
τῶν κρατεροφρόνων         
τοῖς κρατερόφροσι / κρατερόφροσιν         
τούς κρατερόφρονας         
(ὦ) κρατερόφρονες

[Mark Manguno]

Many thanks for the quick answer! Sorry if it was a trivial question; I am but a pathetic monoglot with enough interest in languages to know that I don't know what I don't know, so I didn't want to make any assumptions.

[spiros]

Well, no worries, there are tools in the net which can help you get all the different forms, i.e. https://logeion.uchicago.edu/morpho/