Eureka! was released by CLS Farms — the same operation behind El Dorado — in the mid-2010s, and it stands out immediately for a combination that's genuinely unusual: alpha acid high enough to rival dedicated bittering hops like Warrior or Apollo, paired with an aroma distinctive enough that many recipes still use it for flavor rather than treating it purely as a bittering workhorse.
At 17-21% alpha acid, Eureka! ranks among the highest-alpha hops available, yet its black pepper, marmalade and herbal aroma is specific enough that some brewers reserve a portion of the charge for late-boil or dry-hop use rather than spending the entire addition on pure bitterness the way a neutral high-alpha hop like Magnum typically is. The black pepper note in particular is uncommon among American hops, closer to what's occasionally found in some New Zealand varieties like Pacific Jade than to anything in the domestic Cascade-family lineage.
At an alpha range this unusually high for an aroma-leaning hop, the IBU calculator is worth checking before sizing any charge. Warrior is the closer substitute purely for bittering efficiency, though it lacks Eureka!'s spice and marmalade character entirely. Admiral, an English high-alpha hop with its own marmalade note, is a more aromatically apt substitute despite the different growing tradition. Double IPA and imperial IPA use Eureka! most often, sometimes as a dual bittering-and-late-addition hop in the same recipe.