Red-haired, red-eyed, with three parallel scars on his left cheek, Gojou is a carefree drinking brawling gambling womanizer, evidently without a care in the world. In fact he has a traumatic past. He's a half-breed, son of a youkai father and his human mistress. Such unions are frowned on and semi-forbidden in the Saiyuuki world, being seen as inter-species cross-breeding. The red hair and eyes are the sign of these 'tabooed children.' Gojou was raised by his father's youkai wife. God knows what happened to the father; he doesn't seem to be around. Gojou had an older half-brother, Sa Jien, who appears to have been the one who looked after the boy. Gojou desperately wanted his stepmother's love, but she hated him and cried every time she saw him. (That's why, to this day, Gojou is helpless when faced with a woman in tears.) Obviously an hysteric bordering on the psychotic, she eventually attacked him, ripping his face with her talons (hence the scars) before trying to kill him with an axe. This happened when Gojou was either eight or twelve; Minekura contradicts herself on that point. Young Gojou felt guilty for existing and didn't try to protect himself from his stepmother. 'I figured if I was dead Mom'd stop crying, so it was better this way.' But his step-brother saved him, running his mother through with a sword. Jien, who'd had to endure his own abuse from his hysterical mother, then left, leaving Gojou traumatized and heart-broken.
Gojou grew up somehow to become a footloose drifter, making a precarious living through gambling, and picking up women on a regular basis to get him through the night. Dogged by a sense of guilt about his stepmother and brother, he lived pretty much without real human contacts until one rainy night when the wounded Hakkai fell across his path, quite literally. Seeing he was still alive, Gojou picked him up and half-carried him home, got a doctor to look after him, and let him stay at his place for a month until he was able to move again. Gojou discovered a sense of kinship with the quiet and self-effacing Hakkai, who seemed to be so much his opposite. When Hakkai left Gojou's place, fleeing from Sanzou who'd come to find him and bring him to justice, Gojou followed after him with Sanzou and Gokuu. Later the two moved in together, still very different but somehow managing to become best friends. Gojou has always had the intention of finding his half-brother again, which is one reason he joins Sanzou on his journey to the west.
Alone of the three 'half-youkai', Gojou doesn't need a controlling device to keep him in his human form- since his human form is half youkai to start with ie the eyes and hair colour. (Also the shape of his eyes hints at an unhuman origin.) Nonetheless, unless one knows the marks of the tabooed children, it's natural to assume Gojou is human. Gokuu's regular name for Gojou is erokappa- sexually perverted water spirit. Not that Gojou is a water spirit in any way, but the original Gojou in Journey to the West was. (Gokuu also calls him cockroach head, for reasons unknown. Japanese cockroaches are large and reddish brown, which may have something to do with it.) Gojou isn't perverted, but he's aggressively heterosexual in a way that guarantees his relationships will remain sexual only. 'Love? I don't really know what it is. Never really wanted to. I can get it up even without that...' You can look to his childhood for hints as to why he avoids any deeper contact with women. Gojou's complicated feelings about the woman he feared and whose love he desperately wanted are currently being explored in the series.