A bit of an enigma to the Farscape universe, Crais is a character who had it all and, through disobeying orders, threw it away.
Initially raised by his parents on a farm with his brother Tauvo, their parents looked after both sons and raised them with compassion and emotion. But this did not last, as both Bailar and Tauvo Crais were taken by force to be enlisted into Peacekeeper service.
Both the Crais brothers moved up through the ranks of the Peacekeeper service, but tried to remain as close as possible. Indeed, the death of Tauvo came when he was in command with his brother Bialar, as Tauvo's Prowler hit the Farscape 1 module on Crichton's arrival.
With Bialar being the only Crais brother left, he disobeyed orders and took his command carrier into the Uncharted Territories in pursuit of Crichton and revenge, leaving the rest of his fleet to continue as ordered. This was met with some disagreement, at which he had to kill one of his lieutenants.
When pitted against Crichton by Maldis however, Crais nearly seemed to forgive the human, but relented. It was only when Scorpius found out about Crais disobeying orders in the Aurora chair that Crais seemed to know he had to concede defeat and turn to Crichton's side, admitting that he didn't seek revenge for his brother Tauvo's sake, but for the sake of himself.
However, Crais seemed to find a new friend in the form of Moya's Gunship son Talyn. As Scorpius was approaching Crais decided to take Talyn and escape with him. Since then, Talyn has come to trust Crais, and likewise Crais with Talyn. Talyn even chose Crais over Aeryn to be his companion and implanted Crais with a device that allowed the two of them to share thoughts, effectively making Crais Talyn's Pilot.
However, Crais also had a hand in Talyn's birth and in his genetic abnormalities, as Crais was the one who implanted Moya with the device that D'Argo smashed, leaving her pregnant. Crais is also partially responsible for Pilot as he demanded a new Pilot for Moya as the old one was unwilling to let the Peacekeepers control Moya as they did and use her for their plans.
More recently Crais has been willing to allow Talyn to cause damage in order for the wormhole experiment of Scorpius to be thwarted, and for self-defence. It was Talyn who destroyed the Shadow Depository, and destroyed Scorpius' Command Carrier (ultimately at the cost of Crais and Talyn). Crais also went through strong jealousy towards the Crichton who fell in love with Aeryn, which caused some major rifts.
However, Crais' main objective has been to survive, which was why he kidnapped Talyn in the first place - so that Moya's crew would have to protect him as well to protect Talyn. John uncovered this and confronted Crais over it, with little result.
However, Peacekeeper retrieval squads were sent after Crais and Talyn, to apprehend the traitor and make use of the Gunship technology. Headed by Xhalax Sun, Crais and Talyn were wounded and picked up by Moya, before retreating. Later on Aeryn would convince her mother Xhalax she was wrong, and Xhalax would take her own life.
Helping John sabotage Scorpius' wormhole tech, Crais ran into an old flame, lieutenant Lorell, who spied on him. Crais worked this out, but by that point it was too late for Lorell to do much - Crais destroyed the Command Carrier, himself and Talyn dying with it in a hero's death.