Boston venture capital firm Spark Capital, an early investor in Twitter Inc. and Tumblr Inc., has closed its fourth investment fund totaling $450 million, the firm said Monday. The latest round is Spark’s largest fund and brings the total amount the firm has raised to $1.42 billion. It closed its last round of $360 million in 2010.

“When we started nobody really knew who we were. We were this VC firm above a shoe store on Newbury Street,” said Bijan Sabet, a general partner at Spark. “We’ve just tried our hardest to build our reputation with founders.”