Mr. Rovainen was a researcher aboard Castle Wulfenbach. He is sometimes referred to as "Dr. Rovainen" but his granting institution was destroyed before the degree could be completed.
As it turned out Mr. Rovainen was possibly the worst person that could possibly have been assigned to the hive engine project. He was, in fact, already enslaved, and when Agatha Heterodyne, enraged by his lechery, ordered him to go do " ", he took it as the command to go and (an example of the Mongfish command voice), killing (or "sparing") his friend Dr. Vg in passing. (This implies he is aware that his present state is worse than death and may have a limited ability to act on that awareness.) Evidently he also rerouted the failsafe system so that it would kill anyone who incautiously attempted to kill the wasps.
Presumably, he was among the first revenants discovered by a wasp eater, and his description of his and Agatha's encounter gave Baron Klaus Wulfenbach even more evidence in support of his theory that Agatha was the Other. (Again, it is interesting to note that while being interrogated he was evidently able to speak freely about what he had done and what triggered it.)
Possibly relevant outside information
His name is a Finnish surname. 'Rova' is a rare word that means a rocky mound.
Kaja Foglio revealed that Mr. Rovainen's name was "stolen" from Toivo Rovainen, friend of the Foglios and one-time assembly chief for Cheapass Games, a company run by James Ernest, another friend. Ernest and his company produced The Works as well as a non-Girl Genius game called Deadwood Studios, USA, which features art from Phil Foglio. It was funded via a successful Kickstarter campaign.
Mr. Rovainen might have been seencarrying a trident.