"You cannot possibly be as stupid as you act."
"...Ken if I vants to be!"
- --Master Payne, Oggie
Ognian, aka Oggie, is one of the three "wild" Jägermonsters who help Agatha and friends in all manner of combat situations (combat, after all, being what Jägermonsters are good for). Ognian is the one with relatively normal flesh tones, a single curled horn on the left side of his head, and . Ognian therefore does not wear shoes. He does, however, wear a snazzy fez. (At least at first..)
In battle, Ognian uses a rather unique weapon: a triple-poleaxe. In addition to hewing body parts in twain, Ognian also uses the polearm as a quarter-staff to ward off blows, as a launching-pad for his fellow Jägers to jump off of, and as a vaulting pole to get over obstacles. Pretty handy, no? During the Sturmhalten plot-arc, he also makes good use of this weapon when dealing with Dimo's poisoned/melty arm. Eventually, however, he parts ways with it as he follows Agatha around Europa, and shows that he's quite capable of fighting unarmed.
While Dimo is known for his good nose, Maxim is known for his good ears, and it's Jenka who is given the telescope for a more detailed visual analysis of what's going on over in Mechanicsburg when the group is hanging out at one of the city's external watchtowers, it has been hinted that Oggie with, again, his human-colored skin might have the best sense of touch. It would explain why he's the one who the Sneaky Gate that's presumably hidden to all other senses and whose location can't be predicted, and gives an explanation why he hugs Agatha in the scene where the Jäger are asking her permission to go along with Master Payne's plan to travel through Sturmhalten without incident.
In personality, Ognian is one of the more lighthearted and carefree of Da Boys, much more so than Dimo, whose responsibility makes him more serious, and Maxim, who hides a philosopher's soul under a facade of chivalry. Of the three, he is probably also the most interested in vimmin (again with the touching!) and was in fact married to a biologically normal human during the early decades of his Jägerhood; from his very great-great-grandsons. Having said descendants continue to reproduce is shown to be something of an obsession with Oggie., he has worn a necklace which a portrait of his late as-yet unnamed wife, whom he fondly describes as being a troubadour-type who was ugly in a cute sort of way. This union produced numerous entirely human descendants (as is reportedly always the case with Jägers); again while in Sturmhalten he and we one of his
As confirmed by the image above, he totally doesn't deal with Lars' latest panic attack by punching him in the back of the head, it's a brick from that bridge that blew up. It confesses and everything!
And he has a tendency to blurt out sensitive information at inappropriate times, often being at the receiving end of punches from other Jägers present as a result.
He is separated from Agatha during the Timeskip, but eventually rejoins her at Grandmother's little soiree in Paris, assisting in the fight against the rampaging Storm King by being, well, Oggie. During the cleanup afterwards, he also sort-of battles Parisian governmental minion Abraxus and claims the man's impressive periscope-topped hat as a war-prize. He (and the hat) then travel on with Agatha and the rest of her entourage to England. While in the undersea dome of The Queen's Society, he gets shot by one of Queen Albia's minions who has been suborned by a copy of Lucrezia, and cheerfully drinks something whipped up by Tweedle that gets him in an impressive way... only for him to be stabbed through the chest by the Lu-copy inside Agatha with one of Zeetha's purloined swords. He doesn't die, but he loses the hat, and he's forced to have a little lie-down before fleeing the self-destructing dome with the rest of Our Heroes. The longterm effects of the Tweedle-draught, if any, remain to be seen.
The Mechanicsburg Solstice side-story depicts him living in an Agatha-ruled Mechanicsburg following the end of the Other War, and celebrating that season's festivities with his numerous descendants, including a new in-law.
Possibly relevant outside information
According to Behind the Name, "Ognian" comes from Bulgarian огнен (ognen) meaning "fiery".