Whether someone is "intelligent" or not depends entirely on what you are asking them to accomplish with their brain.
"Intelligence" is from Latin word “intellego” -Inter-lego: Bind together, read between the lines, or connect the dots. Intelligence has been defined in many different ways such as in terms of one's capacity for logic, abstract thought, understanding, self-awareness, communication, learning, emotional knowledge, memory, planning, creativity and problem solving. Intelligence is indeed multidimensional, so how to assess a person’s “intelligence”?
What is your raw intelligence? Generally speaking, everybody has certain “raw intelligence,” independent of their formal education or accumulated experience – an inherent intelligence and an area they're good at or even excel. All humans have their innate capabilities or intelligence: Just like a kind of tablet, one already completed and preserved inside you. Whether they are aware of it and can express it, or not, is a different question. Intelligence is fluid, like fountainhead flows within you, moving out. And such raw intelligence, just like the rough diamond can be sharpened via continuous learning, to shape the differentiated capability which can be both useful to ourselves and benefit others as well.
What makes a person intellectual? In order to get "intelligence," a brain (a dynamic, evolving network of interconnected neurons) must have a certain minimum amount of complexity (complexity is a function of structure, the topology of that network of neurons, and entropy). What makes a person intellectual is the use of his/her intellect, which is the rational, analytical mind. When things are perceived intellectually, then they are looked at from the conscious mind and ordinary awareness, which means a quantifiable, logical, external perspective involving a lot of mental "doing" = thinking, comparing, concluding, reasoning and planning, knowledgeable, articulate, and curious. It's how you think, and how others view your thoughts! Then, you need the intellectual integrity to use that knowledge wisely rather than for your own ends.
How to apply intelligence to solving complex problems? It is our connectedness to the world around us that makes whatever intelligence we have truly useful to ourselves and to others; connected, by a sort of resonance between our cognitive and affective dimensions and the actual world we co-inhabit with those around us. The Intelligence is mainly comprised of two parts. The first part is the brain ability to preliminarily understand the extent of any problem or condition. The people with what being referred as highly intelligent have a strong aptitude to understand the "complexity" of the given problem. It's like a rating scale of complexity. Some people get the whole picture as opposed to others that can't seem to get a grasp on the problem. Now the second part of intelligence is the brain’s ability to call on as many neural circuits and work with as many areas in the brain it needs to solve the given problem.
Intelligence is the quick and clear perception of any situation, plus ability to adjust to any circumstances. It is contextual and multidimensional. Whether someone is "intelligent" or not depends entirely on what you are asking them to accomplish with their brain. Intelligence is continuing with life no matter what, and never allow what you can't do interfere with what you can.