In or about the fifth or sixth century B.C.E., a person named Gautama was born a prince to a royal family in Nepal.

" The future Shakyamuni Buddha*, Gautama, was born in the 5th or 6th century BCE in what is now Nepal. Although historians believe there was such a person, much of his life story seems to be shrouded in legend.

Although we often speak of "the Buddha," there are many Buddhas in Buddhism. On top of that, the many Buddhas come with many names and forms and play multiple roles. The word "Buddha" means "one who woke up," and in Buddhist doctrine, any such enlightened individual is technically a Buddha. In addition, the word Buddha is often used to mean the principle of Buddha-nature. But of course, there is one historical figure that normally is considered the Buddha. 

According to legend, Siddhartha Gautama was the son of a king, and as a youth and young adult, he lived a sheltered and pampered life. In his late 20s, he was shocked to witness sickness, old age, and death for the first time, and he was filled with such dread he resolved to give up his royal birthright to seek peace of mind.

After several false starts, Gautama eventually settled determinately into deep meditation under the famous Bodhi tree in Bodh Gaya, in North Eastern India, and realized enlightenment, at about the age of 35. He was called Buddha, which means "one who woke up." He spent the rest of his life teaching and died at about the age of 80, achieving Nirvana. More detail about the life of Gautama can be read in The Life of the Buddha. "

(the above is adapted and excerpted from this excellent page by Barbara O'Brien Shakyamuni Buddha--The Historical Buddha)

The proceeding is, of my own discernment, the best way of stating the truths he realized and taught:

• dukkha (the nature of sufferings and joys)
• samudaya (causes of sufferings and joys)
• nirodha (the possibility of lessening and preventing sufferings (even unto permanent  cessation) and the earning of joys)
• marga (how to contend with suffering and achieve happiness) in contemporary American English (Four Noble Truths - Wikipedia)
  
  * The term Buddha is not a name but a title, meaning "one who is 'woke', who is enlightened"¹

four truths

1. people may experience good and bad
   
   

2. causes of good and bad are discernible
   
   

3. we could achieve and increase good and lessen, prevent bad
   
   

4. the way to do this is via good efforts, metaphorically walking "the eightfold noble path" (noble - having or showing fine personal qualities or high moral principles and ideals):
   
   

   1. good efforts , "samma vayama" (in the Pali language spoken of by Shakyamuni Gowtama)

   2. true understanding , "samma ditthi"
      
      

   3. buenos intent , "samma sankalpa" (good intentions)

      
      

   4. apropos focus , "samma paya"
      
      

   5. wise action , "samma kammanta"
      
      

   6. compassionate communication , "samma vaca"
      
      

   7. "critical"* thinking , "samma sankappa"

   8. dutiful  awareness , "samma sati"

* The Dalai Lama, quoted in "I Am", the movie:

Question for the Dalai Lama: “What’s the most important [thing] we can do now?”

Answer: “Critical thinking, followed by [such] action. Discern what your world is. [...] And then figure out where your talents might fit in to make a better world.”

(source: https://calvincorreli.com/blog/1957-critical-thinking-followed-by-action)

further elucidation of the eight capabilities common to all