Ben Kingsley might be a good choice, but personally I think his Aslan might be a little too stern.

Ben Kingsley did voice Bagheera in the 2016 Jungle Book, which has me thinking that Christian Bale, who recently voiced Bagheera in the 2018 Mowgli, might be another good idea. His voice is pretty amazing for thay character.

If Liam isn't available, then it needs a voice similar in depth.

Ben's is rich but not deep and low - and he is one of my favourite actors, so I would want him otherwise.

So, here is my problem with Liam Neeson as Aslan. The problem isn't the writing, that's okay until VDT. He does bring the caring, loving, majestic sound to Aslan, the biggest thing that he doesn't bring, is the......I can't find the right word, but the fear, the unpredictability, the respect, the not being tame quality. In the books, Aslan never felt truly safe. When you were with him, you knew that he was good, but he never felt quite, safe. I think that David Suchet brought that a lot of the time, even though he got silly sometimes. That's why Suchet is still my favorite Aslan. That is the biggest thing that I'm looking for in a new Aslan. I don't need a golden voice who can sound big and grand, Aslan is so much more than that. I want someone who can make me feel like I'm not watching a tame lion. (By the way, that's why one of the best Aslan moments in the movies is when he takes out that Telmarine soldier. It was unexpected, and you can see in Lucy's face that even though she knows that he's good, she's not quite sure how safe he is, and that's why it's so good!)
I heard people throwing out Tom Hardy as a name, and I think that he could work really well. He's a good actor, and though he can put on a more whimpy voice, if you're familiar with his work, you know that he can do a grand voice as well.
I would also put Sean Bean as an option that I think could be really good. Some other ideas that I'd like to hear others thoughts on are people like Gerard Butler, and Russel Crowe, Jeremy Irons, Richard Armitage, and Brian Blessed.
Let me know what you guys think of these.

I would also put Sean Bean as an option that I think could be really good. Some other ideas that I'd like to hear others thoughts on are people like Gerard Butler, and Russel Crowe, Jeremy Irons, Richard Armitage, and Brian Blessed.
Let me know what you guys think of these.

Sean Bean is a worthy contender I think. I’ve seen enough range from him that I really think he could pull it off. Russell Crowe is a close second (as far as your suggestions go). I haven’t seen Armitage in anything other than The Hobbit, as far as I can remember. While I like his voice, I’m not confident in his range, simply for a lack of exposure to his work.

In light of the most recent Talking Beasts podcast, I’m beginning the become less concerned for casting than I am for the filmmakers’ vision. If they really comprehend who Aslan is as a character, the casting will likely fall into place. For example, I think Andrew Adamson’s vision for all the characters was clear and he hit the casting on the nail head according to his vision. In his case though, he didn’t properly understand Aslan.

The problem is most filmmakers are looking for the next franchise for a successful career, and while they may be willing to research the prominent characters of whatever adaptation they may be undertaking, few may be willing to take the effort to really understand such an in-depth character, even if they don’t realize they are “being lazy about it”. Aslan is a prominent character throughout the series, undoubtedly, but his scenes from book to book and few and far between in relation to the main characters of each given novel. Therefore he lends himself to the danger of being treated like a Yoda when it comes to a filmmaker’s efforts.

I would also put Sean Bean as an option that I think could be really good. Some other ideas that I'd like to hear others thoughts on are people like Gerard Butler, and Russel Crowe, Jeremy Irons, Richard Armitage, and Brian Blessed.
Let me know what you guys think of these.

I would definitely be in favor of Richard Armitage. He has a great, deep, voice. Plenty of acting range. He can play gentle and fierce with equal skill.

Oh, Brian Blessed could be interesting! He's a bit gruff-sounding though. Have you heard him as the voice of G.A. Henty in the Heirloom Audio Drama series of the Henty books?

I would also put Sean Bean as an option that I think could be really good. Some other ideas that I'd like to hear others thoughts on are people like Gerard Butler, and Russel Crowe, Jeremy Irons, Richard Armitage, and Brian Blessed.
Let me know what you guys think of these.

Not sure whether Brian Blessed has it in him still. But he was always great to listen to.

Crowe? Yes, probably worth looking at.

Butler? - this is rather funny, because in the early days of Narniaweb (pre-casting) there was a big fan lobby for him to play Aslan. In fact we had to abandon an early poll on possible actors, after it became obvious people were multi-voting in a big way! LOL. Some of them claimed that it was just that he was popular. Can't remember the proportions, but his number was well beyond the other likely names.

What would you say to Iain Glen?

Netflix's Aslan needs to be a younger, wilder (and Scottish ) version of the character. I really hope that Aldrich plays up that aspect of Narnia, in general. I think the casting of Aslan can help in setting that tone.

Richard Madden... Make it happen Netflix.

To me, the exact person they cast for Aslan is immaterial, since really it's all about how they modulate his voice in post-production.

A good example of this I feel is in the recent HBO / BBC adaptation of His Dark Materials. In the 2008 movie of the same book (the Golden Compass) they cast Ian McKellan as the Polar Bear, and he just sounds exactly like Ian McKellan does. Its a very similar performance to Liam Neeson's Aslan. i.e. it's fine, its just not particularly "animal-like". By comparison in the new TV series, they cast a complete unknown (Joe Tandberg) but they've modulated his voice in Post-Production to give it a real bear-like quality. By having a voice of such tone and texture that no real human could ever have, it really helps sell the idea that the voice is coming from an animal of that size - rather than just the disembodied voice of a famous actor emanating from a CGI animal.

As mentioned by a few other people, Benedict Cumberbatch's rasping, serpentine like voice modulation they did for for Smaug is probably a good example too.

Has anyone suggested Timothy Dalton yet?

Liam Neeson was really good. I think Kennath Branagh might be an interesting choice. 

As @icarus said earlier (and probably others have too), I think what Aslan's voice really needs is some post-production work to make it sound less human and more, well, lion-like...

Posted by: @icarus

By having a voice of such tone and texture that no real human could ever have, it really helps sell the idea that the voice is coming from an animal of that size - rather than just the disembodied voice of a famous actor emanating from a CGI animal.

I don't think any adaptation of Narnia has done that so far, at least not to any great extent. I remember with Ronald Pickup's voice in the BBC version, they added a little growl-effect behind it at times, which helped somewhat, though I wouldn't say it was perfect (and wherever they got Aslan's roars from, they sounded very unconvincing). I've just checked a few clips of the Walden films online (I've been avoiding them since the first one fell totally flat for me; it still does, even in little bits) and Liam Neeson just sounds like an ordinary human being — no depth, no resonance, no other-worldliness. David Suchet generally does a very good job in the Focus on the Family radio plays, especially in the very quiet and emotional parts, but he still also sounds pretty much human and there are times where I'd say he hams it up a bit too much. I haven't heard the BBC radio versions, so can't comment on them. 

Aslan has got to be a character who strikes awe into your heart the moment he speaks; no normal human voice is going to have that effect on its own. Hopefully they wouldn't overdo the modulation either, to the point where it sounds weird or contrived, but if they can just make whoever's voice it is sound like THE most magnificent, awesome, not-safe-but-good being you can imagine... Particularly when they do The Magician's Nephew and he commands the new world to awake!

And just now I've been revisiting the 1979 animated film of LWW, which I also haven't seen for a long time. They've definitely added some extra resonance to Aslan's voice (this is the British version, with Stephen Thorne as Aslan), and while it still doesn't really sound like I imagine he should, there's at least some sense that this voice is coming from a greater-than-human creature. With modern technology, I'm sure they can do even better than that if they try!

(Oh, and one more thing — anyone from Netflix, especially, if you're reading this — please, please, please... Aslan's name is pronounced ASS-lan. Not AZ-lan. C.S. Lewis himself said so, and he of all people should know!!! )

I almost wonder if it would be possible to layer 2 voices? I think they do need some special effects on a human voice to make it more lionesque.

I feel like Benedict Cumberbatch has such a GREAT voice for a character like this, he has such a range, but at this point he might be too popular? I listen to his audiobooks to sleep, so maybe I’m biased for him at this point ? 

Idris Elba is my personal vote (especially after hearing his voice work in The Jungle Book + Zootopia).