Do firbolg clerics have access to the giant pantheon?

Question

Does a firbolg cleric from the forgotten realms have access to the giant pantheon?

I am looking for an answer from a mechanical standpoint but also from a lore standpoint.

Answer 1

FR wiki refers to the 2e sourcebook Giantcraft and an article from the Polyhedron magazine and states:

In general, firbolgs admired the goddess Iallanis. However, the firbolgs of the Moonshae Isles were an exception to this. They worshiped the demigod Grond Peaksmasher, thought by religious scholars to be the son of Hiatea. While in truth, the firbolgs were descendants of Othea and Ulutiu, the firbolgs of the Moonshaes believed that Grond carved them from stone and that the dwarves were the result of the "leftovers" of this process.

So the lore has examples of firbolgs worshipping giant deities. Iallanis is the giant goddess of love and mercy, her elder sister Hiatea is the giant goddess of nature, agriculture, hunting, females, and children. They are both daughters of Annam and an unknown sky goddess (Giantcraft, page 42).

Answer 2

Ask your DM

The rules in the Player's Handbook are intentionally vague on what deities are eligible to be selected by clerics:

As you create a cleric, the most important question to consider is which deity to serve and what principles you want your character to embody. Appendix B includes lists of many of the gods of the multiverse. Check with your DM to learn which deities are in your campaign

You will have to ask your GM if the deities from the giant pantheon are in your campaign. If so, you can choose them. There are typically no racial restrictions for deity selection unless that specific deity has a policy.

Answer 3

Every cleric has “access” to every deity

As David Coffron’s answer indicates, the DM controls what deities exist at all in your campaign, but if a deity exists, a cleric can worship them and receive spells from them—regardless of their race or place of origin. It might be unusual for a kobold to worship Thor, for example, but there’s nothing that stops them from doing so, if they would like to.

The only real limitation that might exist for an individual is whether or not they have ever heard of the deity in question in order to choose that deity as their patron, so there might be a question of whether or not a given firbolg character would know about a given giant deity—though as ZwiQ’s answer clarifies, it wouldn’t be very unusual for at least some firbolgs to be quite familiar with at least some giant deities.

The only other problem would be if a deity rejects your worship—but since most deities are always hungry for more faith, that’s rarely a concern. Only a few, very obscure, very tightly focused deities—say, the illithid deity Ilsensine—would be likely to do that.

I realize that this may not be exactly what you were looking for—ZwiQ’s answer is more particular to the question of firbolgs and the giant pantheon—but I really wanted to address the title question head-on, because it’s an important thing: everyone has access to every deity. Even unusual combinations are only that, unusual, not actual problems. This is true both out-of-character (in terms of mechanics) and in-character (in terms of lore).