"доволен" is the short form of "довольный" The choice of form depends on the context. Usually you should use a short form when there is an object or a reason of your satisfaction. For example: Я доволен собой (I'm pleased with myself) or Она довольна результатами (She's pleased with the results) But sometimes you can skip the reason Он вечно недоволен = Он вечно чем-то недоволен (He is always displeased with something) Они были усталые, но довольные (They were tired, but pleased) - In this sentence we use the full form because the adjective only subscribes a characteristic without a reason. Sometimes the reason can be specified in the previous sentence. For example: Я принес ей цветы. Она была очень довольна. (I brought her flowers. She was very pleased.)

It's a short adjective. You can find some information here: http://www.russianlessons.net/grammar/adjectives.php http://masterrussian.com/aa041601a.shtml

Also, as you can see in Vera's answer, meaning for "доволен" has changed from "happy" to "pleased" (sometimes it's even more like "proud of"). So you definitely need to be more specific about the context when you need to translate "happy" to Russian because there could be different variants. You can use "доволен" as translation for "happy" if, for example, you are curious about someones satisfaction with something: Вы довольны результатом? = Are you happy with the result? Вы довольны собой? = Are you happy with yourself? But if you are translating "happy" as human emotion, than you better use words like "веселый", "радостный", "счастливый". Are you happy? = Ты счастлив? You look happy = Ты выглядишь счастливым.