What are a few quotes from Othello that demonstrate Iago being each of these things: persuasive, clever, and evil.

In Othello, Iago is like the Devil, a
sly voice that plays upon fear and weakness.  First, he plays the race card against
Othello, but that fails.  Then, he plays the jealousy card against Desdemona and Cassio,
and it works like a charm.  Iago knows that Othello is insecure about his race, age, and
status in the white world.  He especially knows that as a military man, he is
distrustful of women.  So, he invents and elaborate scheme to destroy Othello through
his woman.  When Othello demands proof of her infidelity, Iago
says:

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I do not like the
office:
But, sith I am enter'd in this cause so
far,
Prick'd to't by foolish honesty and
love,
I will go on. I lay with Cassio
lately;
And, being troubled with a raging
tooth,
I could not
sleep.
There are a kind of men so loose of
soul,
That in their sleeps will mutter their
affairs:
One of this kind is
Cassio:
In sleep I heard him say 'Sweet
Desdemona,
Let us be wary, let us hide our
loves;'
And then, sir, would he gripe and wring my
hand,
Cry 'O sweet creature!' and then kiss me
hard,
As if he pluck'd up kisses by the
roots
That grew upon my lips: then laid his
leg
Over my thigh, and sigh'd, and kiss'd; and
then
Cried 'Cursed fate that gave thee to the
Moor!'

This
psychological strategy angers Othello to no end.  Othello has been jealous of Cassio
(who is everything that Othello is not: white, Christian, young).  This shows that Iago
is very clever: he first uses psychological plants before he moves to physical
evidence.

When Othello demands ocular proof, Iago brings
out the handkerchief, the magical symbol of Othello's manhood and source of his
jealousy:

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I know not that; but such a
handkerchief--
I am sure it was your wife's--did I
to-day
See Cassio wipe his beard
with.

Upon proof
that Cassio has the handkerchief, Iago gets Othello to effectively divorce Desdemona and
align himself with Iago.  His plan to kill her is not only persuasive but very clever:
he knows that Othello will be put to death for the crime.  Othello
says,

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Damn her, lewd minx! O, damn
her!
Come, go with me apart; I will
withdraw,
To furnish me with some swift means of
death
For the fair devil. Now art thou my
lieutenant.

Proof
of Iago's evil is easy to come by, but he is no more evil that when he uses his wife as
a pawn in his twisted revenge plot.  He calls
her

Villanous
whore!

And

Filth,
thou liest!

And
then he stabs her.  Pure evil.