I think a character can perform some significant and pivotal act, but still be disappointing in that his/her personality isn't developed, or developed in a satisfying way. Plot isn't everything.
That's very true - especially if one is speaking in terms of long term or even significantly recurring characters (meaning ones that appear in a goodly amount of episodes but aren't necessarily in for the long haul or meant to be the prime focus (like a Jenny Collins, Flora Collins, Mrs. Johnson, etc.) - characters that generally serve a purpose beyond forwarding/illuminating the story). But when it comes to minor characters (meaning those who by most soap definitions have been solely designed to appear in five or less episodes) that becomes much harder for writers to accomplish - and almost by virtue of their extremely short existences, they're there simply to advance the plot or shine a spotlight on some aspect of the plot or of another character.
When it comes to Claude, along with falling into the minor character category, he was meant to be a man of mystery, so it's not all that surprising that everything about him wasn't spelled out. Claude was a character who held the potential to answer questions about Roxanne and her relationship to Angelique and Tim Stokes - and in that respect he totally served his purpose. That he was instrumental in destroying Angelique was simply icing on the cake in terms of plot, but also very satisfying in terms of his character's albeit short personal journey, given his deep regret for what he allowed to happen to Roxanne. Maybe one might have wished to have seen and learned more about him, but the fact that we didn't doesn't in any way mean that he fizzled. Fizzled carries the connotation that a character appeared, had little impact, made little impression, and/or offered little information, and then disappeared, especially failing to manage anything of any significance. Claude was definitely not that type of character. And in fact, if one was intrigued by Claude enough to want to know more about him, apparently some part of him was quite captivating.
As for Dameon, one of his purposes was to be the first to tarnish the Great Myth of Angelique - the notion that seemingly every character up to that point had voiced that she was perfection personified as everything from Mistress of Collinwood to wife. But that facade cracked under the weight of the reality Dameon's appearance illuminated that Angelique had multiple affairs and wasn't even above instigating murder to dispose of admirers of whom she grew weary. And a second purpose of Dameon was to create suspense that he just might have possibly gotten through to Quentin that 1) Angelique was indeed back at Collinwood, and that 2) his life was in jeopardy (as one might recall that Angelique initially wanted Quentin destroyed because she blamed him for her death). Dameon follows through on both those purposes quite successfully - and particularly when it comes to the first purpose I cited, no one can say he had little impact. In fact, his involvement radically shifted the audience's impression of Angelique from that point onward.
Claude and Dameon are but two in a list of minor characters (i.e. Suki Forbes, Julianka, Garth Blackwood, etc.) who served their purposes, and served their purposes well...
Now, if anyone wants to talk about a character who may not have served much purpose - one who is quite possibly the ultimate DS fizzled character completely irrespective to length of stay because he had little impact, made little impression, offered little information, and then disappeared, especially failing to manage anything of any significance - then one should look no further than starting a discussion about Harry Johnson.
But then, we can thank Norma Curtis' infatuation with Craig Slocum for him.
(Apparently the Curtises had questionable taste when it came to the sort of actors who appealed to them enough to want to see characters created for them.
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