Captain Simon Banks (left): Captain of Major Crime,  Jim and Blair's boss. He's divorced and has a  teenage son, Daryl.		Blair Sandburg (right):  Anthropology Grad Student  and Teaching Fellow at Rainier University. He's doing his thesis on SENTINELS and helps the Detective with his senses. He works as a civilian observer in Major Crime and is partnered with Jim in the field.
	Detective James Ellison (middle): Detective with Major Crime and a Sentinel. He is a former Army Ranger  and spent time doing Covert Ops  with Special Forces

Detective Henri Brown	Detective Rafe (aka "Mr. GQ")

Joel Taggart Captain of the Bomb Squad	Megan Connor A visiting officer from Australia

Cassandra Wells Forensics Chief (first half of season 3) (no one liked her much)

What was Ellison doing in Peru and how did he get his senses?
Ellison was a Captain in the Army Rangers on a mission when his helicopter crashed in the Peruvian jungle. He spent 18 months in the jungle and lived with a tribe of natives. His senses are a result of a genetic advantage that remained dormant until he was exposed to the jungle isolation. "Prolonged periods of isolation" can activate dormant Sentinel abilities.

How did Sandburg and Ellison meet?
After Ellison was rescued from Peru, his senses disappeared. He apparently wasn't aware that he had special senses in Peru... either that, or he just didn't remember (trauma). Five years later, while working with the Cascade P.D., he was on a stake-out in the woods for about a week. His senses came back online, but he didn't understand what was happening to him. He sought out medical advice, but no one could help him. Blair Sandburg, the only real authority in the nation on Sentinels, heard about Ellison's medical "problems" and sought the detective out, offering to help Ellison with his senses in exchange for using him as the primary subject of Blair's dissertation.

What is "zoning"?
When a Sentinel concentrates too hard on one sense, he can block out the rest of the senses. In other words, he becomes so focused on that one sensory input that he blocks out the outside world. Zoning can expose a Sentinel to danger because he becomes literally frozen and unaware of potential hazards around him.

What is a Guide?
Blair Sandburg is Jim Ellison's Guide. A Guide is a Sentinel's partner. He watches the Sentinel's back and, if necessary, pulls the Sentinel out of a zone. Guides, it seems, also have shamanistic responsibilities to "guide the animal spirit".

What the heck is the animal spirit?
Hell, If I know! *grin*
Actually, the animal spirit is the source of the Sentinel's sensory powers (yeah, I know it's supposed to be genetic). Apparently, the genes are nothing without the guidance of the animal spirit. Jim's animal spirit is a black jaguar, commonly known as a panther.
The Guide may also have an animal spirit, it seems. Sandburg has been represented as a wolf at times in Ellison's "dream world" so it may be that Sandburg's animal spirit is a wolf.

Who all knows about Ellison's Sentinel abilities?
Ellison, Sandburg, Captain Banks, and, to a degree, Jim's father... not counting a small number of bad guys. None of Ellison co-workers know about his abilities except for Megan in the last season.

Note: The Masculine form is used here  just because Blair and Jim are male.
Sentinels and Guides can be either male or female.