Spike's original moniker, "William the Bloody," in some ways foreshadowed and justified the character's significant transformation throughout his run on Buffy the Vampire Slayer. Though Spike's former name is mentioned early on in the series, it is finally revealed in season 5 episode 7, "Fool For Love," that he was dubbed "William the Bloody" by his peers because of his "bloody awful" romantic poetry. However, there's actually much more significance behind the nickname than a jibe at Spike's lack of lyricism.
Before he gained his fearsome reputation as a vampire, Spike had been a meek, lovelorn Englishman with a passion for words and a dislike for confrontation and violence. That all changed when he met the vampire Drusilla, the first person to truly understand him and treat him kindly. Once Spike had turned, all his anger towards the people who mocked and belittled him was unleashed on the rest of humanity. After a lifetime of feeling invisible and helpless, Spike's heady newfound power almost absorbed him completely. Played by James Marsters, Spike quickly became a fan favorite on Buffy the Vampire Slayer, especially as he began to transition from a featured villain to an aspiring hero and potential love interest for Buffy. While Spike and Buffy's relationship is tumultuous to say the least, the growth of his feelings for her is a huge turning point for his character. As a result, Spike struggles throughout the later seasons of Buffy the Vampire Slayer to reconcile the warring sides of himself: the insecure romantic versus the vengeful misanthrope.
In the end, Spike's romantic nature wins out, which is proven beyond doubt when he sacrifices himself to save Buffy and her friends in the Buffy the Vampire Slayer series finale. Though the character was quickly resurrected to co-star in the fifth season of Angel, Spike's final act on Buffy was one of love and selflessness. Even when Buffy tries to give him everything that he has desperately wanted by telling him that she loves him back, Spike responds: "No you don't, but thanks for saying it." Unlike in earlier seasons where he begs and threatens Buffy to reciprocate his feelings, by the end of season 7 Spike has learned what unconditional and unselfish love really is, and he gives it to Buffy without expecting anything in return. For and because of Buffy, Spike finally accepts and makes peace with the vulnerable, deeply romantic aspects of himself that used to define him back when he was human being taunted with the nickname "William the Bloody."
Though Spike's arc had many problems and missteps over the years due to the problematic Buffy the Vampire Slayer creator Joss Whedon's apparent dislike of the character, he was able to redeem and prove himself in Buffy's eyes by the end of the series. His positive character development was largely driven by his desire to become a good man, which is how he described himself to a woman he loved when he was human, telling her "I know I'm a bad poet, but I'm a good man." Spike's conflict often comes from his longing to have that part of himself back, while not tolerating the reciprocal return of the more fanciful, idealistic parts of himself that had been so mercilessly teased, mistakenly perceived as weak and blundering even by Spike.
However, despite the original plans for Spike, at his core, the character has always been the profoundly romantic and painfully emotional "William the Bloody" awful writer of love poems. While the name brought Spike shame due to the derisive context in which it was given, it is really a testament to Spike's love for love, which he fought to suppress for over a century. The nickname "Spike" originally came from the railroad spikes he used to impale his early victims; however, "William the Bloody Awful Poet" suits the character Spike came to be over the course of Buffy the Vampire Slayer much more aptly.