Kant is widely regarded as as "deontology personified" (Louden 1986, p. 473.) But if we widen our attention from the Groundwork and the Critique of Practical Reason to include his "virtue theory" (Tugendlehre) we find the clear and firm elements of a virtue ethics. The Groundwork and the Critique of Practical Reason are vital elements of Kant's ethical theory but they are not the whole story.
The deontological element in Kant's ethical theory
...Kant's ethics is
often portrayed as overly formalistic, devoid of substantial
content, and without regard for the consequences of actions
or questions of character ... (Claus Dierksmeier, 'Kant on Virtue', Journal of Business Ethics, Vol. 113, No. 4, Special Issue on Putting Virtues Into
Practice (April 2013), pp. 597-609: 597.)
There are prima facie grounds for this view in Kant's texts :
[I]n his Groundworks of
the Metaphysics of Morals, he did write, for example,
(a) that the pure idea of duty was the touchstone of all
ethicality, (b) that ethical action must come from reverence
for moral law, (c) that for the validity of moral actions
considerations of their probable outcomes would be irrelevant, and (d) that hence a lofty disregard for "results" was
the hallmark of a good conscience (AA IV, 393—39. (Dierksmeier: 599.)
The character of the agent, central to virtue ethics, seems to have no place. All that matters is whether an agent's intentional actions fulfil the requirements of duty and proceed from respect for the moral law.
This appears to reckon Kant among the deontologists. Very roughly indeed, a deontological ethical theory is concerned exclusively the requirement to do one's duty, to fulfil one's moral obligations. The demands of duty are independent of one's character, moral sentiments or feelings; duty is done, or not done, according to one's motivation and that motivation derives from one's rational nature, a nature which (unlike your or my character) is universal among human agents.
Kant and virtue ethics
The view outlined above is not a caricature but it is also not a complete picture.
Kant ... wrote a
"virtue theory" (Tugendlehre), wherein he discussed the
questions of character as well as the teleological nature of
human action. Numerous Kant scholars argue that Kant
already erected precisely the kind of integrative moral
architecture that' [virtue ethics desiderates]. (Dierksmeier: 597.)
Once the possibility of valid ethical assessments has been established (as first explored in the Groundwork and then demonstrated in the Critique of Practical Reason), Kant turns to the next project: reconstructing the phenomenology of our moral experiences. This project is advanced in his conceptually rich Metaphysics of Morals, which consists of two major parts: a legal doctrine (Rechtslehre) and a doctrine of virtue (Tugendlehre). In the latter, we find Kant's mature moral philosophy (Timmons 2002). Here he discusses his ethical teachings in depth and detail. Here, too, he argues in favor of many subjects (such as virtue, character, and moral sentiments) for the alleged oversight of which contemporary critics criticize him. So, in the genealogy of his studies, Kant moves from initially predominantly abstract concerns of validity (at the foundational level of this theory) to the questions about the genesis of concrete
moral actions (at the application level). His theory changes accordingly from reflections on the conceptual possibility and moral necessity of categorical imperatives to investigations into the practical reality of their objects and objectives (Höffe 1983).
In his Tugendlehre, Kant wishes no less but to elucidate what constitutes virtuous living in daily practice. In this context, emotions and intuitions find Kant's acute attention. Wherever the phenomenal correlates with the noumenal directives of practical reason, moral sentiments play an eminent role in his theory (Ameriks 2000). For instance, Kant affirms that our intuitions often provide us with important introspective and situational insight (Audi 2001). Contrary to conventional wisdom, Kant's ethics is thus neither bereft of an emotional side, nor of contextual sensitivity (Baxley 2003). On the contrary, his Metaphysics of Morals proceeds as the very analysis of such dimensions of kind of motivation or moral feeling, albeit through universal conceptual standards (Speight 1997). The latter are not meant to eliminate, but to elucidate the former; they relate to one another, as matter does to form. Far from trying to derive ethics out of logical inferences alone (Powell 2006), Kant's concern is not at all — as some of his critics still profess — to avoid particular and sensual motives from entering into the process of our will formation, but solely to determine whether they make us violate moral commitments. (Dierksmeier: 601-2.)
Philip Klöcking has kindly allowed me to add the following material:
I would like to add that if it is the notion of character and how it is formed one is interested in - a concept central to any virtue ethics - one is well-advised to have a look into his Anthropology and Religion as well. His views on this aspect of his "virtue ethics" are much more pointedly described there. Even prolific Kant scholars have the tendency to pretend these two books would not exist or have any meaningful content, although Kant himself states how important this part of his philosophy is in the introduction to the Anthropology.
Maybe to bolster the point: Central statements in the Anthropology are in Ak. 7:285 and 291-295 where he speaks of (moral) character as a way of thinking [Denkungsart] and in the Religion 6:26-28 where he speaks of different predispositions to good, especially in the guise of "predisposition to personality". Also, the essay On the Miscarriage of all Philosophical Trials discusses good character, especially in 8:269-271.
Addendum: In Religion, 6:46-49, he contrasts virtue understood as legally good (habitual/empirical good character) with virtue understood as morally good (intellectual/noumenal good character). The latter is tied to "mode of thought" [Denkungsart] which has to guide the habitual "mode of sense" [Sinnesart]. Essentially, all later works are concerned with how we can become habitually virtuous without ceasing to become morally virtuous, i.e. how we can be moral without having to actively reject inclinations via the CI every time - his answer is character understood as mode of thought.
On 'phenomenal' and 'noumenal' see: https://en.wikipedia.org/wiki/Noumenon.
Reading - date order:
Claus Dierksmeier, 'Kant on Virtue', Journal of Business Ethics, Vol. 113, No. 4, Special Issue on Putting Virtues Into Practice (April 2013), pp. 597-609.
B.K. Powell, (2006). Kant and Kantians on "the normative question". Ethical Theory and Moral Practice, 9(5), 535-544.
A.M. Baxley, (2003). Does Kantian virtue amount to more than continence? The Review of Metaphysics, 56(3), 559-586.
M. Timmons, (2002). Kant's metaphysics of morals: Interpretative
essays. New York: Oxford University Press.
O. Höffe, O. (1983). Immanuel Kant. München: C.H. Beck; (Trans.). (1994). Immanuel Kant. Albany: State University of New York Press,
C.A. Speight, (1997). The "metaphysics" of morals and Hegel's critique of Kantian ethics. History of Philosophy Quarterly, 14(4), 379-402.