The fastest hundred in ODI Cricket was scored by Abraham Benjamin de Villiers (AB de Villiers) of South Africa in 31 balls. The record of fastest hundred in Test Cricket is shared by Sir Viv Richards of West Indies and Misbah-ul-Haq of Pakistan. Both scored hundred in 56 balls. The fastest century in Twenty20 Cricket was scored by Richard Levi of South Africa in 45 balls.
Sanath Jayasuriya(SriLanka) scored 50 off 17 balls against Pakistan in 1996 which is the fastest 50 in limited overs cricket. If you also consider Twenty20 Internationals (which is indeed a form of Limited overs cricket), the record is currently held by Yuvraj Singh (India), who scored a memorable 50 off just 12 balls against England in 2007 during the Twenty20 World Cup.
As of July 2009, Virender Sehwag holds the record for the fastest hundred by an Indian in any form of cricket. He scored hundred in 60 balls against New Zealand in Hamilton on 11th March 2009. This was an ODI cricket match. Kapil Dev and Mohammad Azharuddin are the fastest hundred scorers in Tests for India. Both share this record of 74 balls.
Not only 100,he holds the record of taking fastest 200 wickets as well.
Virender Sehwag (300 of 278 balls)
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The fastest 100 in cricket was hit by Shahid Afridi in 37 balls.
shahid afridi from the Pakistani team
Sir Viv Richards of West Indies has made fastest test century from 56 balls against England in 1985-86 at ST.John's. This record is fastest century by ball. If you see my minutes than it's Jack Gregory of Australia against South Africa. He made his century in 70 minutes in 1921-22 at Johannesburg.
Shahid Khan Afridi, He made 102 Runs in just 37 Balls.
Virender Sehwag holds the record for scoring the fastest triple century in Test cricket. He achieved this milestone in 278 balls against South Africa in 2008.
161.1 by Shoiab Akthar. Then comes Brett Lee and Shaun Tait clocking 160 km/h.