Sam Fisher will be the next Rainbow Six Siege operator. Siege's biggest crossover will bring the grizzled spec ops veteran into Ubisoft's tactical FPS in Rainbow Six Siege: Operation Shadow Legacy, a fitting name for the stealthy but dormant character.
Leaks in June revealed the existence of Sam Fisher in Siege, but the reveal video above confirms him as the next (and only) operator coming in Shadow Legacy. The teaser seems to confirm what we learned in June: Sam is an attacker who will carry some kind of special gadget that fires camera bolts that and burrow through soft walls, allowing him to spot what's on the other side. The leak also suggested that these cameras can deal ranged damage.
If that turns out to be true, Sam could become a useful source of information and harassment, a kind of attacker counterpart to Valkyrie and Maestro.
Reading into Ubisoft's in-character description of Sam Fisher on the Siege website, one might get the sense that Fisher could just be the start of further such cameos coming to Siege. "As he’s coming in as the first member of the Rainbow Operational Staff (ROS), I’m curious and cautious of the changes he’ll bring to our organization." It remains to be seen whether this "Rainbow Operational Staff" is a new subset of operators, or just a bit of flavor text. Maybe we'll find that out when the character is revealed in full this Sunday.