He is voiced by Tetsuya Kakihara in the Japanese version of the anime and Tyler Galindo in the English version, the latter of whom also voices Lubbock.
Rundelhaus is a young, noble-looking boy with blond hair and blue eyes. He has been described as attractive by a few characters, although his popularity is decreased by his somewhat eccentric personality. Isuzu claims he looks like a golden retriever.
Rundelhaus is a brash, flamboyant and boastful person, as well as slightly narcissistic. This is shown when he looked down on Minori for her low level despite being only two levels above her (naturally, Touya chewed him out for this). He has a habit of using English terms when being especially flamboyant. However, he is more than capable of being polite, frequently addressing women as 'Miss' and not hesitating to give credit where credit is due, such as when he complimented Isuzu for combining her Harmony Carol with his Orb of Lava.
Rudy is also overconfident in his abilities and quite naive in certain situations, not knowing that being a Sorcerer doesn't put him on the front lines. He is also shown to not be much of a team player, often unleashing his full power without taking the strengths of his party members into account and taking a while to open up to Minori about his techniques when she was attempting to build a strategy, though he quickly began to see the benefits and sincerely apologised for his initial refusal to cooperate.
Despite his arrogant and flamboyant attitude, Rudy is also rather hardworking, which is shown when Isuzu walks in on him training by himself, having constructed a sparse outline of the Training Camp's dungeon and spending hours directing fireballs. He also becomes flustered when he realizes Isuzu was watching, implying that he's not as confident in his abilities as he lets on. He can also be very heroic in certain situations, being more than willing to give up his life to protect Choushi Town (a drastically more significant sacrifice, because as a Person of the Land, he dies permanently). However, this willingness to sacrifice himself saddens and later angers Isuzu, and after his first resurrection, she chews him out for being so reckless, calling him the biggest idiot she's ever met.
Out of all of the Log Horizon members, while he loves them all, he seems to get along with Isuzu the best, with Touya a close second.
- Of the eight Log Horizon members at the end of season 1, Rudy is one of two Shiroe did not know before the Apocalypse, the other being Isuzu.