Sir Webinar was a warlord in service to King Slately of the Jetstone Tribe. Apparently a loyal, competent warlord with significant melee skills, but perhaps a little single minded in his approach to his role.
Immediately after Jillian Zamussels leaves to fly a scouting mission, Prince Ansom sends for Sir Webinar, giving him orders to assemble a group of seven heavy units and follow Jillian. His mission is ground support, or rescue/recovery if that becomes necessary. He takes Dora, several cloth golems and tchotchkes, and a sourmander and proceeds cross-country in the direction of Gobwin Knob.
After encountering a squad of spidews, losing one of his cloth golems in the battle, he realizes that he hasn't seen any of the enemy's dwagons. He decides to pick up the pace, following a road rather than a cross-country path as per his original instructions.
However, he is too late to provide assistance, and finds Jillian's sword and message hat on the ground where they were dropped before she was captured. Webinar uses the message hat to report this news to Ansom.
Later, Webinar's group finds Jillian, who reports that she has escaped through the tunnels under Gobwin Knob. Webinar and Dora are suspicious of her story, and Webinar goes so far as to accuse her of being a turncoat.
Webinar is later chosen by Prince Ansom to lead the Jetstone and Marbit troops in an attack on the tunnels under Gobwin Knob. Although Webinar is initially doubtful of his qualification he agrees to lead the attack anyway.
The attack fails as a rock golem controlled by Sizemore Rockwell crushes Webinar and Dora.
Soon after, he, along with Dora and the rest of the fallen members of the tunnel force are uncroaked by Wanda Firebaugh. While the majority of the tunnel force are placed on the walls, Webinar and Dora accompany Wanda for a strike against Prince Ansom, where he and Dora are destroyed for good by Archons.
A "webinar" is a type of mostly one-way internet conference: the word is literally a portmanteau of "web seminar".