Ahmed Shehzad was the first Pakistani batsman to score a century in T20 Internationals. He scored against Bangladesh in T20 World Cup 2014.
Chris Gayle of West Indies scored the first century in T-20 Internationals against South Africa in the very first match of the First World Cup(T-20) in 2007.
Demis Amiss of England scored the first century of ODI against Australia in 1972 at Old Trafford. This was the second official ODI match. Amiss scored 103 runs for England.
Chris Gayle of West Indies scored the first ever century in T-20 against South Africa in 2007; the first T-20 World Cup.
On Indian soil he scored his first ODI century at Visakhapatnam against Pakistan in 2005.
Aminul Islam scored first century for Bangladesh in test cricket. He scored 145 runs against India in 10th of November, 2000 at Dhaka, Bangladesh.
Sachin Tendulkar of India.
Kapil Dev scored first Century in ODI for India. His score of 175* against Zimbabwe in 1983 Cricket World Cup is the first century by an Indian in ODI.