Julius "Jayjay" Junior, is a male Silky Sifaka Lemur, first introduced in The Time Paradox. He is three years old, has snowy white hair with brown skin, and is more than a meter long from head to tail. He was named after Julius Root after Mulch Diggums noticed the similar appearances between the two.
Jayjay first appears in Artemis Fowl: The Time Paradox. The Time Paradox begins with Artemis Fowl II discovering his mother is deathly ill. He calls upon his fairy friends, hoping for a magical healing. When Foaly and Holly Short admit that Artemis's mother has contracted a supposed eradicated fairy disease called Spelltropy, and that the only known cure is found in a now extinct Silky Sifaka Lemur brain fluid, Artemis devises a plan to use №1's magic to travel back eight years in time, hoping to save the species. He tricks Holly into thinking that she is the reason why his mother is dying, guilting her into accompanying him on his journey.
When traveling back in time, Artemis Fowl runs into his younger self, age ten, who is also after the species's last lemur, though for other reasons than the elder Artemis (money). Artemis the elder must search hard and fast for the creature before the time travel spell fades, leaving Holly and Artemis stuck in the past forever. Both Artemises exchange the role of the upper hand as Jayjay trades possession more than once.
Artemis the elder meets Jayjay when he is searching for the lemur due to his need for the lemur's brain fluid to save his mother from the fairy disease. It is revealed later in the book that this disease was being caused by Opal Koboi, as a ruse to get Artemis to travel back in time to get Jayjay, whose brain fluid was the last ingredient of "extinct animal's brain fluid" to make her all-powerful.
Mulch, Artemis, and Holly all noticed the resemblance in the hair cut between the lemur and Julius Root, nicknaming him "Julius Junior".