The soldier killed in an attack in London has been named as Drummer Lee Rigby of the 2nd Battalion the Royal Regiment of Fusiliers.
Drummer Rigby, 25, from Manchester, leaves behind a two-year-old son.
Two suspects shot by police after Wednesday's attack in Woolwich remain under arrest. A further two people have been arrested on conspiracy to murder.
The suspects, one of whom is said to be Islamist protester Michael Adebolajo, were known to security services.
Scotland Yard said the latest arrests were of a man and woman, both aged 29.
Drummer Rigby's family issued a statement on Thursday, saying: "Lee was lovely. He would do anything for anybody, he always looked after his sisters and always protected them. He took a 'big brother' role with everyone.
"All he wanted to do from when he was a little boy, was be in the Army.
"He wanted to live life and enjoy himself. His family meant everything to him. He was a loving son, husband, father, brother, and uncle, and a friend to many."
'Popular and witty'
A post-mortem examination was being carried out on Thursday.
The Ministry of Defence also paid tribute to Drummer Rigby.
"An extremely popular and witty soldier, Drummer Rigby was a larger than life personality within the Corps of Drums and was well known, liked and respected across the Second Fusiliers.
"He was a passionate and life-long Manchester United fan."
Drummer Rigby, from Middleton, Greater Manchester, joined the Army in 2006. He was described as a "loving father to his son Jack" and someone who would be "sorely missed by all who knew him".
In other developments:
• The two suspects who were shot remain in separate London hospitals in stable conditions with non-life-threatening injuries
• Video footage, obtained by the Daily Mirror, has emerged of the moment the two men were shot by police
• Six residential addresses are being searched: three in south London, one in east London, one in north London and one in Lincoln
• Items were recovered from the Woolwich scene, police said
• An increased police presence will be in Woolwich and the surrounding areas through Thursday night and "as long as needed", Assistant Commissioner for Specialist Crime and Operations Mark Rowley said
• With dozens of witnesses to the killing, police are urging them to contact the Met's anti-terrorism hotline with information
• US President Barack Obama says his country "stands resolute with the United Kingdom, our ally and friend, against violent extremism and terror"
• Military charity Help for Heroes said since the attack people had been "spontaneously showing support for the armed forces"
• Two men have been charged with separate attacks on mosques, in Kent and Essex, after the death of the soldier
Drummer Rigby had taken up a post with the Regimental Recruiting Team in London in 2011.
"An experienced and talented side drummer and machine gunner, he was a true warrior and served with distinction in Afghanistan, Germany and Cyprus," said his commanding officer Lt Col Jim Taylor.
"His ability, talent and personality made him a natural choice to work in the recruiting group."
Capt Alan Williamson said: "Drummer Rigby or 'Riggers' as he was known within the platoon was a cheeky and humorous man, always there with a joke to brighten the mood."
Defence Secretary Philip Hammond said: "This was a senseless murder of a soldier who has served the Army faithfully in a variety of roles including operational tours in Afghanistan.
"Our thoughts today are with his family and loved ones who are trying to come to terms with this terrible loss."
Mr Hammond was asked if the attack showed how vulnerable soldiers were, whether they were in uniform or not.
He replied: "I think it reminds us how vulnerable we all are, but it also reminds us, by the response of the public, that we are not going to be cowed by this kind of terrorist action."
Chief of Defence Staff General Sir David Richards said: "It's always a tragedy, it's particularly poignant that it happened on the streets of this capital city of ours.
"We're absolutely determined not to be intimidated into not doing the right thing - whether it's here in this country or in Afghanistan or wherever we seek to serve the nation."
Security at Woolwich Barracks and others in London has been increased, and Gen Richards said: "I'm confident that base security is as tight as it's ever been, and necessarily so.
"It's a very difficult balancing act. We are very proud of the uniform we wear, we have huge support around the country, this is a completely isolated incident."
Shortly after the killing, a man, thought to be 28-year-old Mr Adebolajo, was filmed by a passer-by, saying he carried out the attack because British soldiers killed Muslims every day.
Sources said reports the men had featured in "several investigations" in recent years - but were not deemed to be planning an attack - "were not inaccurate".
According to BBC sources, Mr Adebolajo, a Briton of Nigerian descent, comes from a devout Christian family but took up Islam after leaving college in 2001.
The BBC has uncovered its own footage of one of him taking part in an Islamist demonstration in April 2007 against the arrest of a man from Luton.
Mr Adebolajo can be seen standing in a crowd of men outside Paddington Green police station, holding a placard reading "Crusade Against Muslims".
He is standing next to Anjem Choudary, who was the leader of al-Muhajiroun, a now-banned organisation.
Mr Choudary said Mr Adebolajo was previously associated with the group, but went his own way in around 2010.
The Independent Police Complaints Commission sent 12 investigators to look at the scene.
They reviewed CCTV footage from a local authority camera, and said two officers fired shots and one officer discharged a Taser.
One of the shot men received first aid from the firearms officers.
"At this stage we are not pursuing any criminal or misconduct offences," said Commissioner Derrick Campbell.
I think almost the entire nation has been stunned by this sickening attack. R.I.P. Drummer Rigby. :'(