 Other notable characters who have been involved with the Fantastic Four include Alyssa Moy, Caledonia (Alysande Stuart of Earth-9809), Fantastic Force, the Inhumans (particularly the royal family members Black Bolt, Crystal, Medusa, Gorgon, Karnak, Triton, and Lockjaw), Reed's father Nathaniel Richards, the Silver Surfer (previously an antagonist), Thundra, postal worker Willie Lumpkin, Baxter Building landlord Walter Collins, the Thing's rivals the Yancy Street Gang and Uatu the Watcher.Author Christopher Knowles states that Kirby's work on creations such as the Inhumans and the Black Panther served as "a showcase of some of the most radical concepts in the history of the medium".Writers and artists over many years have created a variety of characters to challenge the Fantastic Four.