Jack Dorsey steps down as Twitter chief executive

• Dorsey co-founded site in 2006 and posted world's first tweet
• Parag Agrawal, chief technology officer, to replace Dorsey
• Jack Dorsey: the exiting Twitter CEO with an artist's vision

Twitter co-founder Jack Dorsey has stepped down from his executive role at the social media company.

Dorsey will be replaced by chief technology officer (CTO) Parag Agrawal, the company announced on Monday.