Andy Serkis teases returning characters in The Lord of the Rings: The Hunt for Gollum

Andy Serkis, Gollum himself, will direct the upcoming The Lord of the Rings: The Hunt for Gollum with none other than Peter Jackson as producer. Although the film does not yet have a script ready, he talks a bit about the film in a recent interview with Popverse and he hints that some of the characters we recognise may appear:

"But I will say that it will be a deep dive where we investigate Gollum's character. There may be characters that we recognize that might be coming back. I'm not going to say who."

The most likely to appear is of course Gandalf and Ian McKellen is said to be interested in returning provided he is still alive, something he himself joked about when asked. Whether they have more characters than that in mind remains to be seen, it's pretty important that it fits with the Sméagol/Gollum timeline as well.

Which character(s) do you think might appear in The Hunt for Gollum?