Tim Russ, the actor best known for playing Tuvok in Star Trek, has been confirmed as the voice actor for Sylens in LEGO Horizon Adventures following the sad passing of Lance Reddick, the original voice for the character. It is not known yet whether Russ will be playing the role permanently for the eventual third Horizon title, but Guerrilla Games did previously say the character would be recast starting with the LEGO spin-off.
As well as appearing in Star Trek: Voyager and the more recent Star Trek: Picard as Tuvok aboard the famous starship, Russ has lent his voice to numerous other video game characters, and is not actually even a complete stranger to the Horizon series. He voiced Jetakka in Horizon Forbidden West, a member of the Tenakth tribe who Aloy meets in a few different side quests. Russ has also appeared in a few Bethesda RPGs (Fallout 4, Starfield) and The Last of Us Part II.
Following the very sad passing of Lance Reddick last year, Guerrilla Games paid tribute to him with a memorial found in the Burning Shores expansion for Horizon Forbidden West. Lance also voiced Commander Zavala in the Destiny titles, and he has been succeeded by Keith David in that role.