When the Enterprise NX-01 was first sighted in the Delphic Expanse, Jannar spoke out against rash action, suggesting that the Council simply continue its preplanned course of action and develop the Xindi superweapon. Jannar may have had moral reservations about the construction of the superweapon, but he swept them aside with a "better their world than ours" mentality. He said it was best not to think about how many innocents the weapon would kill, adding, "What we do is for... our children's future. Remember that." (ENT: "The Xindi", "Azati Prime")
However, Jannar voted against the development of the Xindi bioweapon, decreeing that such a move was too dangerous. He believed that Degra must be given more time to create his superweapon. He was very displeased when Commander Dolim had Rajiin infiltrate Enterprise to acquire information on Human physiology and anatomy; he said it put their entire work at risk. (ENT: "Rajiin")
Jannar was very skeptical of wild claims that Captain Jonathan Archer made about the Guardians and their role in building the Delphic Expanse spheres. He came aboard Enterprise with Degra to see Archer's evidence, but constantly pointed out that Archer could be fabricating it. Despite this, he actually could not explain what he was shown; he at least allowed Archer to present his case to the Council. (ENT: "Azati Prime", "The Forgotten", "The Council")
Once Archer did so, Jannar, like Degra, was fully allied with Archer. Arboreal vessels participated on the side of Enterprise in the battle to stop the superweapon from being launched. After the weapon was en route to Earth, Jannar assisted Archer by helping to crew Degra's ship in Archer's effort to catch up to the superweapon in time. (ENT: "The Council", "Countdown", "Zero Hour")
Background information Edit
Jannar was played by Rick Worthy. Despite the character ultimately being canonically named Jannar, Worthy joked with Xindi-Primate actor Tucker Smallwood, one day, that his Arboreal character would be named Chopra while Smallwood's role would be known as Depac, in a light-hearted in-joke reference to the celebrity Deepak Chopra. (; Star Trek: Communicator issue 151, p. 52)
When Rick Worthy auditioned for the role of Jannar, he was pleased to learn that the character would make multiple appearances. "They offered me 10 episodes. I knew it was going to be a recurring role." Worthy was not even dismayed by the extensive make-up required for the part. "I really enjoyed it [....] My character, Jannar, looked a lot like Chewbacca and I thought that was fun."  Worthy also thought Jannar's similarity to Chewbacca was "especially cool." He approved of Jannar in general, saying, "I love [Jannar] as a character as he was intellectual, philosophical and, sort of, a mediator between the two parties."