The German Empire was the main leader of the Central Powers. It had the largest army of the alliance also. When Archduke Franz Ferdinand was assassinated, Germany kept their alliance with Austria-Hungary and would assist them in war against Serbia, as war was looking very promising against the two nations.
The leader of Germany at the time of WWI was Kaiser Wilhelm II. He was the last Kaiser of the German Empire. By the end of the war, he had little military support and not much power. He renounced the thrown and fled the country in 1918.
The Schlieffen Plan was Germany's strategy against the Allies. The Germans were facing both France and Russia, so they wanted to rid France of the war and focus on the Eastern Front. The purpose of the Schlieffen Plan was to gain victory on France by moving through Belgium towards Paris. Because Germany invaded Belgium, breaking the Treaty of London, Great Britain declared war on them.
The Austria-Hungary Empire entered WWI after the assassination of their Archduke Franz Ferdinand. Serbia was blamed and Austria-Hungary declared war.
The leader of Austria-Hungary was Emperor Franz Joseph. His heir to the thrown, the Archduke, was assassinated by a Serbian, so he declared war. Joseph died during WWI and was succeeded by Charles I of Austria.
The Ottoman Empire was a part of the Central Powers because of their German ties. Their 1914 military alliance with Germany called for them to aid the Germans. At the end of WWI, the empire fell and from it formed the nation of Turkey.
The leader of the Ottoman Empire was Sultan Mehmed V. He also died before the end of the war.
Bulgaria was the fourth and last major country to enter WWI for the Central Powers (other countries fought in WWI for the Central Powers, but did not contribute as much). Serbia held land that Bulgaria claimed, so they were eager to go to war.
Ferdinand I was the Tsar of Bulgaria during WWI. After the war, he stepped down and gave the thrown to his son, Boris III.