Marcus

"OK, Marcus," the First Kidnapper said to the Second Kidnapper. "They're not telling, but the Boss said the Heir to the Hairy Hooligans is a weedy-looking kid - which one is he then?" The Second Kidnapper pointed at Hiccup. "It must be that one with the red hair, he said. "Look at him, he's got arms like spaghetti!"

- First and Second Kidnappers, speaking in Latin

Marcus is a Roman appearing in How to Speak Dragonese, Book 3 in the How to Train Your Dragon Book series. He is referred to by Hiccup as the "Second Kidnapper".

Kidnapping the Hooligan Heir
The Romans, specifically the Fat Consul and Thin Prefect, devise a 'Fiendishly Clever Plan', which is to kidnap the heir to the Bog-Burglar Tribe and blame it on the Hairy Hooligan Tribe, and kidnap the Hooligan heir and blame the Bog-Burglars. The two Tribes would be distracted and fight amongst themselves, while the Roman Dragon rustlers grab all the dragons in the Inner Isles of the Barbaric Archipelago. The First Kidnapper and Marcus are tasked with grabbing the Hooligan heir - Hiccup - disguised as Bog-Burglars, who are a Tribe of women.

First and Second Kidnappers burst into the Great Hall in Hooligan Village, while the Viking novices are in 'Frightening Foreigners' class. The First Kidnapper pins Gobber to the wall with an axe by his beard. In broken Norse, both men demand the heir be handed over. No one offers up Hiccup, so the Kidnappers take both Hiccup and Fishlegs, as both are "weedy-looking". They sail away from Berk in a small Roman boat into the Mazy Multitudes and into Fort Sinister to hand over Hiccup and Fishlegs to the Fat Consul and the Thin Prefect.

Physical Description
Marcus is a very large adult male. Under his disguise as a warrior woman, he appears to be balding on his pate, and have some beard stubble, though Romans are depicted without facial hair in the Book series.

"But these were clearly big hairy muscly men in dresses with pigs' bladders stuffed down their blouses instead of bosoms."

- Book 3

Abilities
Marcus knows Norse well enough to communicate to Vikings.