Sis Tak is perhaps the most venerable Word Bearer dreadnought there is. At the very least he's one of the oldest. He started life as a Terran, got drafted for the Great Crusade, and was a veteran long before Lorgar was found. Mortally wounded in battle, he was among the first Astartes to be entombed within a Dreadnought. When the 10th Chapter (now Host) was formed he was added to the roster to bring experience, wisdom - and firepower to the fledgeling Chapter. Sis Tak spends most of his days slumbering and meditating. He's fairly sane and a source of much wisdom. He also has the ear of many of the older veterans.