There are three accounts for the Alarick spelling: 12 in 2015, 5 in 2013, and 5 in 2001. For the Alarik spelling there has been a little more consistency: 6 in 2003, working its way up to 20 in 2015. Lastly, the Alaric spelling is much more popular, used since at least 1949 (7 births that year) to its all-time high of 181 boys given the name in 2015. Alarich, a form sometimes used in Germany, has not been seen on the U.S. graphs, nor has Italian Alarico. Aleric is also sometimes recorded. The name had already been slowly rising, but note a jump between 40 births in 2010, 50 in 2011, and then 88 in 2012. This is likely thanks to The Vampire Diaries, which began airing in 2009. The character Alaric Saltzman is a history teacher and vampire hunter who befriends a vampire and impacts all of the characters for the better.
Alaric I and Alaric II were Visigoth kings who ruled between c. 370 and 507. Another Alaric was king of the Swedes, who shared his kingship with his brother Eric. His name is also spelled Alrek, Alrik and Alric in certain accounts. Alrekr is the Old Norse form, while Alareiks is the original Gothic form.
In modern times, namesakes include Medal of Honor recipient Alaric Chapin, British journalist Alaric Jacob, Liberian politician Alaric Tokpa, American composer Alaric Jans, and British poet and journalist Alaric Alexander Watts. A film director from Singapore born Tay Liang Hoong goes by Alaric, and an English writer born Harold Jacob was known as Alaric.
As for literary references other than Alaric Saltzman, P. G. Wodehouse had a character named Alaric in Blandings Castle, Alexander Theroux's main character in Darconville's Cat was an Alaric, there is a character by the name in Katherine Kurtz's Deryni series, an Alaric in The Bird Artist by Howard Norman, and Stephen King even used the name in the Dark Tower series. Possibly the oldest literary namesake is Alaric Tudor, a clerk in Anthony Trollope's The Three Clerks, published in 1857. You might also like Sir Alaric, Keeper of the Kings Records, a Dr. Seuss character in "The 500 Hats of Bartholomew Cubbins. Also, Alaric is in the title of a book, sort of, in the Tales of Alaric the Minstrel - a couple of books with individual titles by Phyllis Eisenstein.
Ulric, Ullrich and Ulrick are not other forms of the name Alaric. They are originally from Odalric, a Germanic name meaning "prosperity and power."