The Hero Trilogy Imagines

Answer

So. The answer was gotten in about an hour by TimeTravelingMew - it was the Boss. CONGLATURATION.

Imma do a stanza by stanza thing. I wouldn't blame you for skipping this chapter.

In this riddle
You must seek
A character's name
In the rhymes I speak

This one just tells you that you're looking for a character's name.
———
A widower is
The name you require
He is neither hero of water
Nor man of fire

So you're looking for a widower. The definition of widower is; a man that has lost his spouse (person he is married to) by death and has not married again That basically narrows it down to two people; Matthew or the Boss.

The second part of it just bluntly tells you that it isn't Dan or Phil.
———
Oppressed rage
Lies beneath
He'll let it loose
No room to think

'Oppressed rage lies beneath' - yeah we see a lot of anger in him

'He'll let it loose, no room to think' - to him, spending time to think about what he's doing and why he's doing it isn't important to him and he's already come so far so there's no point in sitting down and thinking about it.
———
As the clock ticks down
He has a choice
The next man up
Or another voice

'As the clock ticks down' - he's dying. He doesn't have much time left.

'He has a choice, the next man up or another voice' - his choice is whether to give Cry (the next man up) control of the Institute when he dies or to give it to Mr Vincent (another voice)
———
And with his choice
He lets go
His dreams; destroyed
Or helped to grow?

'And with his choice, he lets go' - he dies after he gives it to Vincent, he's handed off his responsibility

'His dreams; destroyed or helped to grow?' - he's just gambled on whether or not his dream of revenge were struck down or fulfilled by who he gave the Institute to

•••

Ok so, genuinely, I don't remember writing the riddle. I don't know what I was thinking, I just have 'answer to riddle: Boss' written in one of my notebooks so ok then. This is my attempt at recreating my thinking.

Wait I have to update now don't I?