Heru was a character from Lieutenant Gullivar Jones: His Vacation, a book written by Edwin Lester Arnold that predated the Barsoom series by Edgar Rice Burroughs and shares many similarities with it, but not nearly as successful. Heru was the love interest of the main protagonist Gullivar Jones, an Earthman that flew to Mars on a magic carpet. She had appeared in comics featuring Jones with her her first appearance being on Marvel's Creatures on the Loose which adapted the book's adventures. Her character was incorporated many years later in Dynamite Entertainment Warriors of Mars miniseries, alongside, where she is established as the mother of Dejah Thoris - probably as a reference to both characters being Martian princesses that fall in love with the heroes from Earth, its fitting that they are made into relatives, with the preceding character serving as the mother for the following one.
Her physical appearance are drastically different between major publications. In her Marvel incarnation, she has green hair and golden skin, while in her Dynamite incarnation, she has black hair and reddish-copper skin. Both versions of her character are noted to be exquisitely beautiful and dressed in revealing, exotic garments.
Heru was a princess of the kingdom of Seth on Mars, she was one of the Hither people, a race that resembled humans from Earth, but with golden skin and green hair. She was betrothed to her distant cousin, Prince Hath, due to them being the last two true golden ones with royal blood to rule Seth until their enemy, the Red Barbarians and their king Ar-Hap, who forced them to pay tributes. Ar-Hap would take the most beautiful maidens of the realm as concubines for an entire year and chose Heru as his next one. Before she could be dragged away, she was saved by Gullivar Jones who was brought to Mars by a mysterious old man and smitten with her beauty, instantly decided to save her.
Heru is now a Red Martian rather than a gold-skinned Hither, and Hath is her father instead of her husband. She still rails from the city-state of Seth, which is at war with the Thithers, a monstrous race. Hath considered the Thithers to be nothing more than animals to be hunted, and the Thithers in turn were highly xenophobic and isolationist, their costume dictates they should never leave their lands and are privy to those that come near them. Heru met Jones when he saved her from drowning.
She was kidnapped by Ar-Hap, King of the Thithers, during a celebration feast made in Jones' honor. Her capture served as a warning for her father to end the aggression between both races. However, Jones went on a quest to save her. Because of his pale skin and blonde hair similar to a Thern, he was regarded as a White Martian or a ghost by the Thithers. Jones used this to his advantage to trick Ar-Hap into releasing the princess and return her home safely. When the Thithers found out he was no spirit, they launched an massive attack on Seth. Heru was told to escape while her father and his warriors fought against their enemies, she kissed her beloved Jones before parting ways with him forever.
Her home was destroyed and her father was killed while murdering Ar-Hap in combat, and Jones himself was presumed dead during the battle. She found her way to Helium and married Mors Kojak, chieftan and son of Jeddak Tardos Mors, and gave birth to two children - Dejah and Kajak Thoris. While she was happy with Kojak, deep down Heru always loved Jones and had fond memories with him. Because Helium was at war with Zodanga, Heru had to give up one of her children as hostages to ensure the peace between the two city-states and surrendered Kajak. Years later, while Dejah was still a child, Heru was poisoned and killed by supposedly agents of Yorn, another rival state of Helium. But it was later revealed that her killer was none other than her own son Kajak, who murdered her in revenge for delivering her to Zodangans.
Many centuries later, Heru was brought back to life by the mysterious power of the carpet that brought Jones to Barsoom in the first place. When her daughter was captured by the Thithers (who wanted to discover how the carpet works, Dejah wished to see her mother again for at least a little time and the carpet heed her wish. Heru appeared and explained her time was limited, and the rug decides which wish is granted within its power. Heru is briefly reunited with Jones, who had survived thanks to the rug's power and appeared several years after in Barsoom, and thanks to John Carter they all escape the Thither' domain. Heru said goodbye to her daughter and gave one last kiss to Jones before fading forever into the afterlife from whence she came.
Early in Dynamite's Warlord of Mars, Dejah Thoris off-handedly remarks about her mother still being alive and waiting for her to return to Helium, despite Heru being long dead by the time Dejah met John Carter. Dejah's mother is never shown or named in either comics or the novels. This was an mistake of the writers who forgot to account Heru, though its entirely possible they didn't consider introducing her in the canon at that point.