Siegfried is a herdsman in Kingdom Come: Deliverance II.
He can be potentially encountered during the side quest Mutt if one tries to do all objectives in it and doesn't find Mutt by exploring. In this case, he'll tell Henry of a local wolf pack that a stray dog has been seen with and asks you deal with them. Sadly though, Mutt is not among them.
Later on, the task, Sheep among Wolves, comes up and to seek him out. If you already assisted him earlier when trying to find Mutt, he'll be happy to see you're back and then directs you where to find this other set of wolves.