Ibn Sina (known to Europeans as Avicenna) was a scientist who was born about 980 AD in the north-eastern part of the Abbasid Empire, in the kingdom of the Samanids (modern Uzbekistan). The Samanids supported science and art, and many scientists and artists lived there. Ibn Sina's father was the Iranian governor of a local village, and was himself a respected scholar. Ibn Sina grew up speaking Persian, like many educated people in that part of the world. He was a very smart child, who memorized the whole Quran by the time he was seven years old, even though it was in Arabic, which was not his first language. While he was still young, he learned about the new Indian number system from traveling teachers. By the time Ibn Sina was eighteen, he was a successful doctor who treated many patients successfully, working in the same town as the earlier scholar Al Razi.
Ibn Sina became so famous as a doctor that the Samanid emir (the prince Nur ibn Mansur) came to him when he was sick. When Ibn Sina cured the emir's sickness, the emir gave him a job as his personal doctor - Ibn Sina was still only 18 years old. As the emir's doctor, Ibn Sina got to read many rare books in the emir's library.
But in 999 AD, when the Samanids were conquered by the Ghaznavids, the Ghaznavids turned out to not be so supportive of science. Ibn Sina left his home and traveled further west, looking for rulers who wanted to support him.
Ibn Sina had many new scientific ideas. For instance, when he was twenty, Ibn Sina was the first person we know of who realized that "impetus was proportional to weight times velocity." This is the basic equation that describes momentum today. He also argued that an object moving in a vacuum would keep moving without slowing down, which is also true. Ibn Sina also said, correctly, that scientists would never succeed in turning metals like lead or copper into gold, even though many scientists were trying to do it.
Ibn Sina also wrote medical textbooks in Arabic, which doctors like Maimonides used all over the Abbasid Empire and (once they had been translated into Latin) all over Europe too all through the Middle Ages. Ibn Sina may have been the first person to realize that you could catch diseases like measles or smallpox or tuberculosis from other people (though he didn't know about germs, because there weren't any microscopes yet).
Ibn Sina died in Iran in 1037 AD, when he was fifty-eight years old, of some sort of digestive problem.